U.S. DEPARTMENT OF THE INTERIOR U.S. GEOLOGICAL SURVEY PRELIMINARY GEOLOGIC MAP OF THE LITTLE PIUTE MOUNTAINS, SAN BERNARDINO COUNTY, CALIFORNIA: A DIGITAL DATABASE By Keith A. Howard, Michael L. Dennis, Karl Karlstrom, and Geoffrey A. Phelps Open - File Report 97-693 This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards or with the North American Stratigraphic Code. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. This database, identified as "Preliminary Geologic map of the Little Piute Mountains, California: A digital database," is the database from which the hard-copy map OF95-598, "Preliminary Geologic map of the Little Piute Mountains, California" was produced. It has been approved for release and publication by the Director of the USGS. Although this database has been subjected to rigorous review and is substantially complete, the USGS reserves the right to revise the data pursuant to further analysis and review. Furthermore, it is released on condition that neither the USGS nor the United States Government may be held liable for any damages resulting from its authorized or unauthorized use. Introduction The Little Piute Mountains Digital database contains digital geologic and geographic information for the study area. The geology was mapped at a scale of 1:8,000, and the topographic information was input from the Little Piute Mountains, CA 1:24,000 quadrangle. The accuracy of the spatial information is limited to the input scale. Postscript files, originally published in paper format as Open-file map 97-693, have been included for those who do not have access to a geographic information system. The files are equivalent to those which produced the hard-copy open file. They can be printed on any device equipped to print postscript files of the appropriate file size. Geologic Summary The Little Piute Mountains in the eastern Mojave Desert expose a series of folds and thrust faults involving metamorphosed Paleozoic strata (Miller and others, 1982; Stone and others, 1983). Detailed mapping of these structures was undertaken to help elucidate regional Mesozoic structural evolution. Earlier geologic maps were prepared by Cooksley(1960a,b,c,d, generalized by Bishop, 1964) and Stone and others (1983). Deformed and metamorphosed Paleozoic and Triassic rocks form a stratal succession that was originally deposited in shallow seas on the North American craton. Based on lithologic sequence the units are correlated with unmetamorphosed equivalents 200 km to the northeast in the Grand Canyon, Arizona, and 35-50 km to the west in the Marble, Ship, and Providence Mountains, California (Stone and others, 1983). The Paleozoic sequence rests nonconformably on a heterogeneous basement of polydeformed Early Proterozoic gneiss (Miller and others, 1982); Wooden and Miller, 1990). Triassic and older rocks were deformed, metamorphosed to staurolite or andalusite grade, and intruded concordantly at their base by Late Cretaceous granodiorite (Miller and others, 1992). (from the Open-File report; references available in the complete report, available in html format as of97-693.html) DATABASE CONTENTS The digital database consists of the geologic map database itself and the supporting data, including a fault map, base maps, map explanation, geologic descriptions, symbolsets and references. All files except ASCII files are in Arc/Info Export format. This format can be read by many commercial GIS packages, and is a way to access the Arc/Info geodatasets without having the Arc/Info software. Arc/Info Geodatasets: The geologic map database consists of two ARC coverages: lp_geo Polygon coverage of geologic faults, contacts, geologic units of the Little Piute Mountains. lp_str Point coverage containing the structural information for the Little Piute Mountains. Point data includes planar and linear structural symbols (strike & dip), line data includes fold axes and lineaments. Annotion is included for the point symbols. The database directory also includes the following supporting directories, ARC coverages, and files: xsec_arc Line coverage of the four cross-section lines used to make cross-sections A through D. Annotation for the ends of the cross-section lines is included. lp_leadr Line coverage of the annotation and annotation leaders for geologic unit annotation in the coverage lp_geo. Annotation is stored in the subclass units. lp_hyp line coverage of the hypsography for the Little Piute Mountains, with attached elevation database. lp_hyd line coverage of the hydrography for the Little Piute Mountains. lp_base Line coverage of the combined base layers for the Little Piute Mountains, no attached database. Annotation relevant to the base is stored in the subclass margin. lp_tin TIN (triangular irregular network) of the Little Piute Mountains constructed from a subset of elevation data from the lp_hyp coverage. Cross-sections: lpxs_a thru d Polygon coverages of geologic cross-sections for the Little Piute Mountains, sections A through D, including geologic faults, contacts and units. lpxs_a thru dan Annotation coverage, including leaders, for the geologic cross-secion coverages A through D. Annotation is included in subclass margin. Lookup tables (INFO files): lppoly.lut Lookup table for geologic units, to be used in conjunction with alc1.shd to reproduce the geologic unit colors of the open-file lpline.lut Lookup table for geologic lines, used to reproduce geologic line symbology of the open-file lppoint.lut Lookup table for geologic marers, used to reproduce geologic marker symboloby of the open-file Symbolsets: key.geology Keyfile used by the program lp_plot.aml to create a list of geologic units present on the geologic map. This is not a correlation chart. For correlation chart information see the text accompanying the map. fnt027 Geologic font which contains special geologic letters (e.g. Cambrian, Proterozoic) fnt038 Geologic font which contains geologic point symbols (e.g. lineation, strike & dip, foliation) fnt040 Geologic font which contains geologic markers that ornament geologic lines (e.g. teeth on faults) alc1.shd Arc/Info shadeset used to color geologic units lpiute.lin Arc/Info lineset used to symbolize lines of the open-file geology.mrk Arc/Info markerset used to symbolize points of the open-file lpiute.txt Arc/Info textset containing geologic letters, used to annotate geologic units on the open-file fontsize.txt Arc/Info textset used for map margin annotation Files: of97-693.html HTML of the text portion of OF97-693, contianing geologic background, history, and unit descriptions. Figures accompanying the text are included as TIF files: figure1.gif GIF image of the location map of the Little Piute Mountains, figure 1, page 4, of the of97-693 text, linked to of97-693.html. figure2.gif GIF image of the correlation of map units for the Little Piute Mountains, linked to of97-693.html. figure.tif TIF image of the legend of lines and structure symbols for the Little Piute Mountains, not linked to of97-693.html. readme A text-only ASCII file containing database specifics. (this document). lpiute.ps A Postscript plottable file containing an image of the geologic map of the Little Piute Mountains at a scale of 1:10,000 (OF 97-693 plate 1). lp_xs.ps A Postscript plottable file containing an image of the Little Piute Mountains cross-sections at a scale of 1:10,000 (OF 97-693 plate 2). disclmr.fil ASCII file that contains the standard open-file disclamer. This file is used as input by the plotting AMLs discussed below. Programs: The following programs were written in AML Arc/Info's macro language, to create plot files of the geologic database. The amls included will reproduce plates 1 and 2 of the open-file report. It is not necessary to run the programs in order to generate a postscript file (the postscript file can be downloaded separately). The AMLs are included for completeness. They can also serve as a reference guide for plotting any derivative map the user may wish to create using the available data. lp_plot.aml The program to create a duplicate of the open-file postscript plot plate 1, lpiute.ps. lpx_plot.aml The program to create a duplicate of the open-file postscript plot plate 2, lp_xs.ps. plot_xs.aml Program run by lpx_plot.aml. padscale.aml Program which creates a scale bar, run by both lp_plot.aml and lpx_plot.aml. The database was compiled in ARC/INFO, a commercial Geographic Information System (Environmental Systems Research Institute, Redlands, California), and is stored in ARC coverage format (ARC/INFO version 7.0.3) in a UNIX tar file. A tar file utility is therefore required to extract the database from the tar file, and GIS software that can read the Arc/Info Export file format is required to access the geologic database information. The digital compilation was done using versions 5.0.1 to 7.0.3 of ARC/INFO. Cross-section coverages were constructed with the help of version 3.0 of the menu interface ALACARTE (Fitzgibbon and Wentworth, 1991, Fitzgibbon, 1991, Wentworth and Fitzgibbon, 1991). Postscript Plot Files The database is in ARC coverage format, and therefore requires use of ARC/INFO or another compatible GIS system to access the information contained within it. For those interested in the geology of the Little Piute Mountains, but who don't use an ARC/INFO compatible GIS system, we have included both the postscript files for the hard-copy open-file (97-693). Two files are included: lpiute.ps -Geologic map, OF 97-693 PLATE 1 4.9 MB uncompressed postscript file lp_xs.ps -Geologic cross-sections, OF 97-693 PLATE 2 1.02 MB uncompressed postscript file Because this release is primarily a digital database, the plot files (and plots derived therefrom) have not been edited to conform to U.S. Geological Survey standards. Small units have not been labeled with leaders and in some instances map features or annotation may overlap. However, sample plots by the authors have proven to be quite legible and useful. compressed tar files The data is stored in two tar files, compressed with the publicly available gzip utility. The contents and sizes of the tar files are as follows: plots.tar.gz gzip-ed tar file, 1.7 MB compressed, 12 MB uncompressed. Contains the files listed under the Files heading and the Postscript Plot Files heading. of97-693.tar.gz gzip-ed tar file, 3.4 MB compressed, 14 MB uncompressed. Contains the files listed under the headings Arc/Info Geodatasets, Lookup tables, Symbolsets, Programs, and all files except the postscript plot files. OBTAINING DIGITAL DATA An approximately 3.7 MB compressed (using the gzip utility) tar file of the database and related files can be obtained 1) from the U.S.G.S. Western Region Cooperative Geologic Mapping Program web site: http://wrgis.wr.usgs.gov 2) by anonymous ftp over Internet, ftp wrgis.wr.usgs.gov 3) by sending a tape to the U.S.G.S. 1) To obtain the tar file from the web site, do the following: open URL http://wrgis.wr.usgs.gov/pub/open-file/of97-693/ click on the datasets you would like to download *WARNING!* Make sure you have enough space for the download. 2) To obtain the tar file by ftp, log in to your UNIX system and do the following: cd local_directory -go to a directory to receive the tar file ftp wrgis.wr.usgs.gov -make ftp connection with the USGS computer WRGIS Name: anonymous -use "anonymous" as your user name Password: your name -use your own user name as password cd pub/geologic -go down to the pub directory cd ca/of97-693 -go down to the open-file directory type binary -change transfer type to binary get of97-693.tar.Z -copy the compressed tar file across Internet to your directory quit -close the ftp connection 3) Send a tape with request and return address to: Little Piute Mountains Database c/o Keith Howard U.S. Geological Survey 345 Middlefield Road, M/S 975 Menlo Park, CA 94025 Do not omit any part of this address! The compressed tar file will be returned on the tape. The acceptable tape types are: 7.0 GB, 8 mm Exabyte tape. EXTRACTING THE DATABASE FROM A COMPRESSED TAPE ARCHIVE (tar) FILE: If you obtained the database on tape: put the tape in your tape drive cd local_directory -go to a directory to receive the tar file tar xvfb /dev/rmt 20 -/dev/rmt is the tape device and 20 is the blocking factor; this puts the tar file in local_directory gzip -d of97-693.tar.gz -makes an 8.2 MB uncompressed tar file of97-693.tar cd local_directory2 -go to the directory that will hold the workspace hfg (if different from local_directory) tar xvfb {path to tar file}/of97-693.tar 20 -extract the hfg workspace from the tar file. If you obtained the database by anonymous ftp: gzip -d of97-693.tar.gz -makes an 8.2 MB uncompressed tar file of97-693.tar cd local_directory2 -go to the directory that will hold the workspace hfg (if different from local_directory) tar xvfb {path to tar file}/of97-693.tar 20 -extract the hfg workspace from the tar file. This process will create a directory "/of97-693" that contains the databases and supporting files as described above, in Arc/Info export format. ARC/INFO EXPORT FILES Database files (Arc/Info geodatasets and look-up tables) of the above datasets are stored in Arc/Info EXPORT format. These files can be recognized by the .e00 extension. Arc/Info EXPORT format is a format read by many GIS packages, and may be converted back to Arc/Info datasets using the IMPORT command. For converting the files into other commercial GIS packages, consult the package's documentation. DIGITAL COMPILATION System Compilation of the geodatasets began in ARC5.0.1 and completed in ARC7.0.3. Tracing was done in ink onto stable base material (mylar) and scanned using a Tektronix 4991 monochrome scanner with a resolution of 304.8 dots per inch. The Tektronix 4991 vectorizes automatically, so no raster images were present. Digitizing was performed on a Calcomp 9100. The bulk of the work (after hardware upgrade) was performed on a SUN SPARC10 workstation running Solaris 2.3. Projection The geodatasets created for the Little Piute Mountains are in a common projection. The projection of the map is as follows: Projection POLYCONIC Units METERS Spheroid CLARKE1866 Parameters: longitude of central meridian -115 3 45.00 latitude of projection's origin 34 37 30.000 false easting (meters) 0.00000 false northing (meters) 0.00000 This information can be obtained with the DESCRIBE command in ARC. The original base map did not have enough pre-defined latitude and longitude locations to define the map projection (it was an enlargement and therefore included only part of the original quadrangle base map), so the UTM grid, zone 11, locations were used as places to locate the "tics" for the geologic coverage. The UTM locations were converted to their polyconic equivalents using the PROJECT command in ARC, and the tics for the coverage were defined based on these locations. Subsequent digital datasets were registered to these tics. Geologic Geodatasets The geologic map information was scanned from a copy traced on stable base material (mylar) and updated by digitizing information from field maps. The input scale of the geologic map information is 1:8,000. The original base map, and the base map for the field sheets, was a 24,000 scale quadrangle map photo-enlarged to 1:8,000. I) lp_geo The geologic coverage lp_geo contains the geologic unit information for the Little Piute Mountains. It is a polygon coverage of geologic units bounded by unit-bounding lines (concealed faults are not included, since they are not unit-bounding lines). Line direction is significant for arcs which represent thrust faults. Annotation is not included in this coverage. The AAT is defined as follows: COLUMN ITEM NAME WIDTH OUTPUT TYPE N.DEC 1 FNODE# 4 5 B - 5 TNODE# 4 5 B - 9 LPOLY# 4 5 B - 13 RPOLY# 4 5 B - 17 LENGTH 4 12 F 3 21 LPIUTE_GEO# 4 5 B - 25 LPIUTE_GEO-ID 4 5 B - 29 LTYPE 35 35 C - geologic line type 64 SEL 1 1 I - extra field 65 SYMB 3 3 I - extra field The PAT is defined as follows: COLUMN ITEM NAME WIDTH OUTPUT TYPE N.DEC 1 AREA 4 12 F 3 5 PERIMETER 4 12 F 3 9 LPIUTE_GEO# 4 5 B - 13 LPIUTE_GEO-ID 4 5 B - 17 PTYPE 35 35 C - geologic unit type The PTYPE field contains the formation name. In many cases the formation name involves characters that are not in the standard keyboard character set e.g. Cambrian. Below is a chart of meta-characters used in place of the geologic characters. For example, in the PTYPE field, Triassic Moenkope formation is coded as #m. To make database queries, search on the metacharacter according to the list below. A special textset, lpiute.txt, contains the geologic characters, and the meta-characters are mapped to them. This allows for the display of the geologic characters during plotting. Proterozoic & Cambrian { Pennsylvanian @ Triassic # Paleozoic $ Mesozoic } II) lp_str The structural information for the Little Piute Mountains is contained in the point coverage lp_str. Attitudes, stored as point locations, and structural lines (e.g. fold axes) were input by digitizing from the mylar base map and from field sheets. Attitudes store the strike or azimuth in a database field called STRIKE, and the dip or plunge in a database field called PLUNGE. The interpretation is dependent upon the type of attitude, stored in the PTTYPE (point type) field. The PAT has an elevation item associated with each point, obtained from the TIN. This elevation value was used to project the attitude information into the plane of the cross-sections. The AAT is defined as follows: COLUMN ITEM NAME WIDTH OUTPUT TYPE N.DEC 1 FNODE# 4 5 B - 5 TNODE# 4 5 B - 9 LPOLY# 4 5 B - 13 RPOLY# 4 5 B - 17 LENGTH 4 12 F 3 21 LPIUTE_STR# 4 5 B - 25 LPIUTE_STR-ID 4 5 B - 29 LTYPE 35 35 C - geologic line type 64 SEL 1 1 I - extra field 65 SYMB 3 3 I - extra field The PAT is defined as follows: COLUMN ITEM NAME WIDTH OUTPUT TYPE N.DEC 1 AREA 4 12 F 3 5 PERIMETER 4 12 F 3 9 LPIUTE_STR# 4 5 B - 13 LPIUTE_STR-ID 4 5 B - 17 PTTYPE 35 35 C - 52 DIP 3 3 I - Attitude dip or plunge 55 STRIKE 3 3 I - Attitude strike or azimuth 58 SEL 1 1 I - extra field 59 SYMB 3 3 I - extra field 68 ELEV 4 12 F 3 Attitude elevation (derived from the TIN) The transformation error is as follows: Scale (X,Y) = (203.393,203.111) Translation = (-2036.147,6612.429) Rotation (degrees) = (90.444) RMS Error (input,output) = (0.009,1.865) ic id input x input y output x output y x error y error ------ ---------------- ---------------- ---------------- ---------------- 1 27.638 31.856 4399.978 946.962 -0.650 -0.598 3 2.694 2.637 -1502.774 6061.464 -1.215 -0.531 4 3.022 32.136 4496.145 5945.997 -1.026 -0.478 5 2.854 17.402 1496.705 6003.730 1.923 0.187 6 17.460 2.466 -1560.489 3061.965 -1.672 0.148 7 17.619 17.241 1438.991 3004.270 3.685 1.213 8 17.785 31.966 4438.432 2946.576 -1.219 0.692 9 27.474 17.111 1400.537 1004.629 0.175 -0.632 III) cross-sections lpxs_a through lpxs_d The cross-sections for the Little Piute Mountains were created from the digital geologic and hypsographic coverages using cross- section tools present in Alacarte. A topograhphic profile coverage, complete with geologic line and unit demarcations, is created in the projection of the geologic coverage. This coverage is treated as if it were x-z space, the "z" direction is the y direction of the projection. The section is placed near the projections origin such that the beginning of the section line is at the x-origin, and the y-axis represents the z-value of the topographic profile in meters above sea level. Height can therefore be measured directly in the coverage, as can distance from the begining of the cross-section line. Once the topographic profile and information regarding where the geologic units intersected the profile were created, the subsurface geology was interpreted by the geologists and added to the coverage by digitizing. The subsurface interpretation is constrained by surface information only. The attribute tables are defined for the first cross-section coverage. They are identical for the remaining three coverages, except for the coverage name. The AAT is defined as follows: COLUMN ITEM NAME WIDTH OUTPUT TYPE N.DEC 1 FNODE# 4 5 B - 5 TNODE# 4 5 B - 9 LPOLY# 4 5 B - 13 RPOLY# 4 5 B - 17 LENGTH 4 12 F 3 21 LPXS_A# 4 5 B - 25 LPXS_A-ID 4 5 B - 29 LTYPE 35 35 C - geologic line type 64 SEL 1 1 I - extra field The PAT is defined as follows: COLUMN ITEM NAME WIDTH OUTPUT TYPE N.DEC 1 AREA 4 12 F 3 5 PERIMETER 4 12 F 3 9 LPXS_A# 4 5 B - 13 LPXS_A-ID 4 5 B - 17 PTYPE 35 35 C - geologic unit type Base Geodatasets The original hard-copy base map was a mylar greenline of the lower east portion of the Little Piute Mountains 24,000 scale quadrangle, photo-enlarged to 1:8,000. The digital base information was obtained from film positives or tracings of this base. I) lp_base The composite base coverage was scanned and vectorized on a SCITEX scanner from a stable mylar copy of the 1:8,000 large-scale base map and delivered as a digital product to one of the authors (G. Phelps). The coverage has been projected and "clipped" slightly to match the final boundary of the Little Piute Mountains geologic layer. The base layer contains no attatched database informaion. The quality of the scan is generally poor and is provided for visual reference only. Transformation error for lp_base Scale (X,Y) = (203.356,203.104) Translation = (-1972.126,-72.326) Rotation (degrees) = (0.024) RMS Error (input,output) = (0.005,1.113) ic id input x input y output x output y x error y error ------ ---------------- ---------------- ---------------- ---------------- 1 31.335 5.025 4399.978 946.962 -0.299 -0.005 2 1.834 5.584 -1598.944 1062.298 -0.755 -0.592 3 2.317 30.200 -1502.774 6061.464 -0.678 -0.144 4 31.813 29.636 4496.145 5945.997 -1.410 -0.427 5 17.079 29.921 1496.705 6003.730 1.699 0.365 6 2.028 15.434 -1560.489 3061.965 -0.596 0.359 7 16.790 15.152 1438.991 3004.270 1.889 0.101 8 31.528 14.870 4438.432 2946.576 -0.323 0.054 9 16.590 5.307 1400.537 1004.629 0.472 0.288 II) lp_hyp The hypsography layer was traced in ink onto mylar from the 1:8,000 large-scale mylar base map, then scanned and transformed. A database was created and the lines were subsequently "tagged" according to their elevation. The elevation units are meters, the contour interval is 10 meters. The line database (lp_hyp.aat) contains two user-defined items: ELEV and SFTYPE. ELEV contains the elevation, in meters, and SFTYPE contains the surface feature type (used when creating surface models) and all lines are defined as 2, though the lines themselves were not used in the final version of the TIN. The AAT is defined as follows: COLUMN ITEM NAME WIDTH OUTPUT TYPE N.DEC 1 FNODE# 4 5 B - 5 TNODE# 4 5 B - 9 LPOLY# 4 5 B - 13 RPOLY# 4 5 B - 17 LENGTH 4 12 F 3 21 LPIUTE_HYP# 4 5 B - 25 LPIUTE_HYP-ID 4 5 B - 29 ELEV 6 6 I - Elevation, in meters 35 SFTYPE 1 1 I - Surface feature type Transformation error for lp_hyp Scale (X,Y) = (203.365,203.015) Translation = (5962.861,-111.397) Rotation (degrees) = (89.453) RMS Error (input,output) = (0.009,1.740) ic id input x input y output x output y x error y error ------ ---------------- ---------------- ---------------- ---------------- 1 5.137 7.736 4399.978 946.962 -0.374 0.424 2 5.407 37.241 -1598.944 1062.298 -0.769 0.973 3 30.026 37.004 -1502.774 6061.464 -1.073 -0.787 4 29.767 7.500 4496.145 5945.997 -0.627 1.019 5 29.904 22.242 1496.705 6003.730 1.165 1.688 6 15.247 37.142 -1560.489 3061.965 -0.135 -1.138 7 15.113 22.378 1438.991 3004.270 2.452 -1.276 8 14.974 7.644 4438.432 2946.576 -0.980 -2.396 9 5.276 22.484 1400.537 1004.629 0.341 1.492 III) lp_hyd The hydrography layer was traced in ink onto mylar from the 1:8,000 large-scale mylar base map, then scanned and transformed. User-defined items ELEV and SFTYPE were added to the database for the purpose of including the streams as features in a surface model. All ELEV entries are -9999 (nodata, the value for z-less breaklines) and SFTYPE has entries of 3 and 5, for hard breaklines and hardreplace, respectively. The database entries have no significance other than their usage in creating a surface model. The AAT is defined as follows: COLUMN ITEM NAME WIDTH OUTPUT TYPE N.DEC 1 FNODE# 4 5 B - 5 TNODE# 4 5 B - 9 LPOLY# 4 5 B - 13 RPOLY# 4 5 B - 17 LENGTH 4 12 F 3 21 LPHD_POL# 4 5 B - 25 LPHD_POL-ID 4 5 B - 29 ELEV 6 6 I - Elevation, null values 35 SFTYPE 1 1 I - Surface feature type transformation error for lp_hyd Scale (X,Y) = (203.372,203.085) Translation = (-2063.249,6963.798) Rotation (degrees) = (90.163) RMS Error (input,output) = (0.007,1.522) ic id input x input y output x output y x error y error ------ ---------------- ---------------- ---------------- ---------------- 1 29.524 31.867 4399.978 946.962 0.381 -0.110 2 29.052 2.362 -1598.944 1062.298 -0.740 -0.014 3 4.437 2.766 -1502.774 6061.464 -0.532 -0.588 4 4.905 32.259 4496.145 5945.997 -1.728 0.449 5 4.670 17.531 1496.705 6003.730 2.600 0.067 6 19.203 2.520 -1560.489 3061.965 -1.471 0.384 7 19.439 17.286 1438.991 3004.270 2.023 0.353 8 19.680 32.019 4438.432 2946.576 -1.403 -0.557 9 29.288 17.120 1400.537 1004.629 0.870 0.016 Triangular Irregular Network (TIN) lp_tin The tin for the Little Piute Mountains was constructed with data from the hypsography coverage. Since the density of information in the hypsography coverage varies, the information (ie: contour lines) was separated into two coverages, roughly according to the break in slope at the base of the mountains. The arcs in each coverage were densified, and the more sparsely spaced contour lines sampled every 350 meters, while the densely space contour lines were sampled every 25 meters. The boundary between the two contrasting areas cause artifacts, known as sliver polygons. The surface model is less accurate in those areas. Spatial Resolution Uses of this digital geologic map should not violate the spatial resolution of the data. Although the digital form of the data removes the constraint imposed by the scale of a paper map, the detail and accuracy inherent in map scale are also present in the digital data. The fact that the geologic database was edited at a scale of 1:8,000 means that higher resolution information is not present in the dataset. Plotting at scales larger than 1:8,000 will not yield greater real detail, although it may reveal fine-scale irregularities below the intended resolution of the database. Similarly, where this database is used in combination with other data of higher resolution, the resolution of the combined output will be limited by the lower resolution of these data. Note that in contrast to the geologic coverages, the base map layers have a resolution of 1:24,000, so significant discrepancies with the geologic coverages are possible. The base map layers are provided for reference only. References Cited Bishop, C.,B., 1964, Needles sheet: California Division of Mines and Geology, Geologic Map of California, Olaf P. Jenkins edition, scale 1:250,000. Cooksley, J.W., Jr., 1960a, Geology and mineral resources of Township 6 North, Ranges 17 and 18 East, San Bernardino base and meridian, San Bernardino County, California: San Francisco, Southern Pacific Land Company, scale 1:24,000. Cooksley, J.W., Jr., 1960b, Geology and mineral resources of Township 7 North, Ranges 17 and 18 East, San Bernardino base and meridian, San Bernardino County, California: San Francisco, Southern Pacific Land Company, scale 1:24,000. Cooksley, J.W., Jr., 1960c, Geology and mineral resources of Township 6 North, Ranges 19 and 20 East, San Bernardino base and meridian, San Bernardino County, California: San Francisco, Southern Pacific Land Company, scale 1:24,000. Cooksley, J.W., Jr., 1960d, Geology and mineral resources of Township 7 North, Ranges 19 and 20 East, San Bernardino base and meridian, San Bernardino County, California: San Francisco, Southern Pacific Land Company, scale 1:24,000. Fitzgibbon, T.T., 1991, ALACARTE installation and system manual (version 1.0): U.S. Geological Survey, Open-File Report 91-587B. Fitzgibbon, T.T., and Wentworth, C.M., 1991, ALACARTE user interface - AML code and demonstration maps (version 1.0): U.S. Geological Survey, Open-File Report 91-587A. Miller, C.F., Howard, K.A., and Hoisch, T.D., 1982, Mesozoic thrusting, metamorphism, and plutonism, Old Woman-Piute Range, southeastern California, in Frost, E.G. and Martin, D.L., Mesozoic-Cenozoic tectonic evolution of the Colorado River region, California, Arizona, and Nevada (Anderson-Hamilton volume): San Diego, Cordilleran Publishers, p. 561-581. Stone, Paul, Howard, K.A., and Hamilton, Warren, 1983, Correlation of metamorphosed Paleozoic strata of the southeastern Mojave Desert region, California and Arizona: Geological Society of America Bulletin, v. 94, p. 1135-1147. Wentworth, C.M., and Fitzgibbon, T.T., 1991, ALACARTE user manual (version 1.0): U.S. Geological Survey, Open-File Report 91-587C. Wooden, J. L and Miller, D.M., 1990, Chronologic and isotopic framework for Early Proterozoic crustal evolution in the eastern Mojave Desert region, SE California: Journal of Geophysical Research, v. 95, p. 20,133-20,146.