New Mexico Bureau of Mines and Mineral Resources
801 Leroy Place
Socorro, NM 87801
Telephone: (505) 835-5487
Fax: (505) 835-6333
Recognizing that modern, accurate hydrogeologic map information provides essential base data for government planning and scientific studies, the New Mexico Bureau of Mines and Mineral Resources (NMBMMR) is now in its sixth year of an aggressive geologic mapping program. Designed to address compelling socioeconomic issues (dwindling water supply and quality, geologic hazards, land-use planning, mineral resources) facing the rapidly growing population in the Middle Rio Grande Valley, 7.5-minute quadrangles are prioritized by the 29-member New Mexico Geologic Mapping Advisory Board, and then funded by the USGS National Cooperative Geologic Mapping Program's (NCGMP) STATEMAP component. For the last four years, NMBMMR has been the most successful state geological survey in the country competing for STATEMAP funds, and by July 1999, we will have mapped 36 7.5-minute quadrangles at either 1:12,000 or 1:24,000.
Unlike many state geological surveys, NMBMMR's digital cartography program evolved slowly through the mid-1990s. Given the rapid rate of STATEMAP quad mapping that developed at this time and the complexity of the geologic coverage, the NMBMMR needed to establish a digital cartographic methodology to develop and distribute high-quality, detailed, multicolor geologic map data to the public as quickly as possible. As a result, a new open-file digital map series (OF-DM) was established in 1997. These OF-DM quads are open-filed for immediate output and consist of a surficial geologic map with explanatory text, unit descriptions, correlation charts, and geologic cross sections.
After attending the Digital Mapping Techniques '97 (DMT '97) conference in Lawrence, KS, we decided to model our digital cartographic production program after that of the Nevada Bureau of Mines and Geology (see Tingley and others, 1997), thereby integrating our Arc/Info-based GIS section with our Macintosh-based Cartography section. This methodology (described below) provided users with digital Arc/Info coverages and/or ink-jet color plots that conformed to our long-established map standards. Combining these platforms allowed us to benefit from the relative elegance of Mac-based graphics programs with the high-end GIS capabilities of Arc/Info. Furthermore, this combined method expedited our overall cartographic production. Months of trial-and-error digitizing and interaction between geologists and technicians were replaced by a single scanned image that could be quickly drafted. In about two weeks, the 1:24,000 Alameda geologic quadrangle went from an inked mylar to a multicolor plotted map sheet, complete with cross sections.
After the geologic data are compiled from field mapping, aerial photo interpretation, borehole cuttings, electrical-conductivity log correlations, etc., geologic linework (contacts, structures, and symbology) is inked onto a mylar greenline stable base and scanned at 100% at 400 d.p.i. on an Intergraph Anatech large-format drum scanner. The image is initially pre-scanned and the scanning software, Scansmith, while holding all of the inked linework drops out the greenline base data. The resulting scanned TIFF file is geo-referenced to a projected geographic grid of latitude and longitude in Arc/Info and then exported as an Adobe Illustrator formatted file to a Macintosh Power-PC. After opening the TIFF scan/grid file on a Background layer in Macromedia FreeHand 8.0, the quadrangle neatline and the graticules of latitude, longitude, and UTM are carefully traced from the scanned original onto a map base layer. The process is then repeated for the geologic contacts, essentially eliminating introduced hand-digitizer errors. Each type of contact is drafted onto separate layers as lines composed of smooth Bézier curves (being defined by two end points and two curve handles). This method of line generation is superior to that of Arc/Info, which can only draw straight-line segments between nodes. Complex linework is generated from a minimum number of Bézier curve points (nodes), thereby minimizing map file size. After the contacts are drafted, structures are traced from the scan onto their own layers in the same manner. Additional layers contain strike and dip and other symbols, which are drafted on the horizontal, directly above those on the scan, and then precisely rotated by entering the exact symbol azimuth into the rotation angle dialog box of the Transform panel.
When the linework is complete, contacts and structures that create geologic map unit contacts are "cloned." These lines are then closed into polygons, separated into layers based upon map unit designation, and assigned CMYK color values that correspond to a developed Arc/Info shadeset based upon USGS/NMBMMR cartographic standards. At this stage, each individual layer (attached to the grid) is exported from the Macintosh back to Arc/Info via MAPublisher 3.0, which exports each layer as individual ArcView shapefiles.
The final stage of digital map production for plot-on-demand paper maps, as well as postscript raster output, involves setting type and collar information in Macromedia FreeHand and attaching the topographic base to the geologic quadrangle. In Adobe Photoshop 4.0, the USGS digital raster graphic file for the specific topographic quadrangle is cropped to the neatline, cleaned, and exported as a TIFF file. In Macromedia FreeHand, it is then rendered transparent, screened to 60% black, and attached to the map file by aligning it upon the grid. The quadrangle is then rasterized in Image Alchemy and plotted on an Encad Novajet plotter on demand.
The OF-DM quadrangles are selected by the New Mexico Geologic Mapping Advisory Board, consisting of geologists, hydrologists, and planners from federal, state, tribal, and local governments, as well as the private sector. The board bases priorities on socioeconomic importance, which currently revolves around stressed water resources. To date, quads chosen for OF-DM mapping are located in a) the Albuquerque basin, b) the surrounding mountain lowland communities of the East Mountain area to the east of Albuquerque, and c) the Santa Fe area, particularly where rapid development is occurring south of the city.
Geologic mapping has been concentrated in the Albuquerque basin due to the current concerns over ground-water availability and quality in New Mexico's largest metropolitan area. The USGS is leading an impressive cooperative effort (the Middle Rio Grande Basin Study -- MRGBS) among various federal, state, tribal, and municipal agencies to gather and interpret geographic, hydrologic, and geologic data in order to identify, quantify, and better manage the region's water resources. Approximately 20 of our 36 total STATEMAP 7.5-minute quads lie within the MRGBS area. These are complemented by 12 NCGMP FEDMAP quads and 2 NCGMP EDMAP quads. Subsurface (borehole, geophysical) data are incorporated into these STATEMAP quads, thus greatly enhancing their value for MRGBS hydrogeologic modeling and model refinement.
At the northern end of the basin in the Placitas area, NMBMMR is conducting an extensive water resources assessment for Sandoval County. The Placitas 7.5-minute quadrangle (OF-DM 2), mapped at 1:12,000, is the cornerstone underlying these studies. The area extends from the basin across rift-margin faults into the Paleozoic and Proterozoic bedrock of the northern terminus of the Sandia Mountains. Ground water is found in a series of confined and unconfined, compartmentalized aquifers, where faults behave as both barriers and conduits for ground-water flow. In a setting of such geological complexity, OF-DM 2 has provided the framework for a thorough hydrogeochemical and hydrologic sampling and monitoring program designed to evaluate locations and rates of mountain front recharge, delineate aquifer zones, characterize water quality, and assess resource sustainability given current and future development trends.
Finally, basin STATEMAP quadrangles are being utilized by NMBMMR to compile a 1:50,000 map of the greater Albuquerque metropolitan area, depicting both surface and subsurface geology. This compilation will provide a series of critical, accurate Arc/Info coverages for input into the city's GIS database. Given the direct applicability of this digital product for ground-water resource sustainability assessment, it is greatly anticipated by city and regional planners.
In the mountain lowland communities east of the Sandia Mountains and Albuquerque, rapid development of largely upper class subdivisions (complete with approved planned golf courses) has recently caused water demand to exceed the carrying capacity of local aquifers. Landowners in the adjacent Estancia Basin (a closed basin to the east) are currently pumping large volumes of ground water to these East Mountain communities to meet these increasing demands. In April of 1998, county officials placed a moratorium on further subdivision development until ground-water studies of the region can be undertaken.
Not unlike Placitas, the East Mountain area is characterized by complex structural and stratigraphic controls on ground-water flow between mountain recharge areas and adjacent basins and these are poorly understood. A hydrogeologic consultant, who represents the commercial ground-water utilities in the Estancia Basin, has proposed that this recharge flowing off the eastern slope of the mountains flows unimpeded through faults to the Estancia Basin. He states that such a ground-water path exists because these faults are low angle, representative of a decollement that headed in the mountains to the west. If true, this suggests that recharge of deep Estancia Basin production wells may be adequate to prevent ground-water mining; if not, such potential consequential problems of a permanently lowered water table, a decline in water quality, and ground subsidence will likely result. New Mexico Office of the State Engineer (NMOSE) personnel have disagreed with the consultant, claiming that the ground-water flow is strongly influenced by high-angle bedrock structures, and instead flows into the Rio Grande basin along the Tijeras fault zone. The key to this debate involves characterization of the geometry of sedimentary strata and crosscutting faults. Our mapping has shown that the faults are high angle and, in fact, are more impressive in geometric complexity, width, and intensity of brittle fracturing than previously thought. As a result, NMOSE has introduced two of our new OF-DM quadrangles as evidence into the water rights hearings.
Rapid growth is also occurring in and around the capital city of Santa Fe. Although Santa Fe itself relies largely upon surface water for municipal and domestic uses, the growing suburbs are pumping ground water. Development is proceeding at an alarming rate south and west of the city where ground water resources are scarce. In Santa Fe, shallow wells have recently become contaminated and water rationing was implemented in 1996. The city of Santa Fe, the county of Santa Fe, the NMOSE, and private consultants have all realized that they need modern, detailed surface and subsurface geologic data before decisions controlling growth are made. We are currently working on our third and fourth STATEMAP-funded 7.5-minute quadrangle maps in the capital area. In several years we will have covered most of the area of critical concern.
In the last six years, NMBMMR has been pursuing an aggressive STATEMAP geologic mapping program, averaging over six quads per year at an average cost of $18,240 per quad. Given this rapid rate of mapping, and the fact that these maps were specifically located in areas deemed most socioeconomically critical, where city officials, planners, consultants, and scientists need modern, accurate digital geologic data, we were faced with developing a cartographic production methodology that allowed rapid dissemination of map data while maintaining established map standards. Thanks in part to the interactions of geologists and cartographers at DMT '97, we feel that we have now successfully met this methodological challenge by combining Arc/Info GIS capabilities and accuracy with the amenities of speed, appearance, and simplicity implicit in Macintosh-based graphics.
Tingley, S.L., Chaney, R.L., and Pizarro, K.A., 1997, Adobe Illustrator for Macintosh -- A cartographic solution at the Nevada Bureau of Mines and Geology, in Soller, D.R., ed., Proceedings of a Workshop on Digital Mapping Techniques: Methods for Geologic Map Data Capture, Management and Publication: U.S. Geological Survey Open-File Report 97-269, p. 27-30.
U.S.Department of the Interior, U.S. Geological Survey
Maintained by Dave Soller
Last updated 10.07.98