The oldest rocks in the quadrangle are Archean high-grade gneiss, and granitic to ultramafic intrusive rocks that are as old as about 3.0 Ga. The gneiss includes a supracrustal assemblage of quartz-feldspar gneiss, amphibolite, quartzite, and biotite schist and gneiss. The basement rocks are overlain by a platform sequence of sedimentary rocks as old as Cambrian Flathead Quartzite and as young as Upper Cretaceous Livingston Group sandstones, shales, and volcanic rocks.
The Archean crystalline rocks crop out in the cores of large basement uplifts, most notably the "Madison-Gravelly arch" that includes parts of the present Tobacco Root Mountains and the Gravelly, Madison, and Gallatin Ranges. These basement uplifts or blocks were thrust westward during the Laramide orogeny over rocks as young as Upper Cretaceous. The thrusts are now exposed in the quadrangle along the western flanks of the Gravelly and Madison Ranges (the Greenhorn thrust and the Hilgard fault system, respectively). Simultaneous with the west-directed thrusting, northwest-striking, northeast-side-up reverse faults formed a parallel set across southwestern Montana; the largest of these is the Spanish Peaks fault, which cuts prominently across the Ennis quadrangle.
Beginning in late Eocene time, extensive volcanism of the Absorka Volcanic Supergroup covered large parts of the area; large remnants of the volcanic field remain in the eastern part of the quadrangle. The volcanism was concurrent with, and followed by, middle Tertiary extension. During this time, the axial zone of the "Madison-Gravelly arch," a large Laramide uplift, collapsed, forming the Madison Valley, structurally a complex down-to-the-east half graben. Basin deposits as thick as 4,500 m filled the graben.
Pleistocene glaciers sculpted the high peaks of the mountain ranges and formed the present rugged topography.
The dataset may be downloaded in either ARC/INFO export format (.e00 files) or ARCView shapefile format. A printable PDF version of the map is also available. The dataset consists of four coverages (ENNISGEO, ENNISFLT, ENNISSYM, and ENNISATT) and a .tiff file containing the scanned USGS topographic basemap. The coverages containing both arc and polygon or point entities, ENNISGEO/ENNISATT, have been divided into two separate sets of files in the ARCView shapefile format named ENNISGLN/ENNISALN and ENNISGPT/ENNISAPT for the line and point entities respectively. All coverages contain the standard ARC/INFO items in addition to the items defined in more detail below. -------------------------------------------------------------------------------- ENNISGEO: Polygon coverage containing all contacts and known or approximated fault lines along with unit label points. PAT Item Definitions: UNIT_SYM is a character item defining the geologic unit represented by each polygon using the unit abreviations defined in the accompanying pamphlet (Proterozoic = !, Cambrian = _, Pennsylvanian = &, and Triassic = @) SHADE_SYM is an integer item defining the cartographic color of each polygon from the shadeset ctr269.shd **************************ennisgeo.pat****************************************** COLUMN ITEM NAME WIDTH OUTPUT TYPE N.DEC ALTERNATE NAME INDEXED? 1 AREA 8 18 F 5 - 9 PERIMETER 8 18 F 5 - 17 ENNISGEO# 4 5 B - - 21 ENNISGEO-ID 4 5 B - - 25 SHADE_SYM 3 3 I - - 28 UNIT_SYM 8 8 C - - Record CASE# FREQUENCY UNIT_SYM SHADE_SYM 1 1 2 0 2 2 2 !Abg 109 3 3 8 !Abs 71 4 4 2 !Agg 107 5 5 7 !Aif 118 6 6 1 !Amd 88 7 7 5 !Ams 72 8 8 30 !Aph 69 9 9 14 !Ass 155 10 10 6 !di 99 11 11 108 &Mqa 246 12 12 25 Aag 127 13 13 182 Aam 155 14 14 26 Abh 97 15 15 4 Abm 132 16 16 5 Abs 159 17 17 7 Agd 201 18 18 14 Agg 65 19 19 16 Agn 102 20 20 11 Agp 85 21 21 6 Ags 114 22 22 1 Aif 99 23 23 24 Ama 84 24 24 34 Amb 88 25 25 27 Aq 172 26 26 246 Aqf 91 27 27 15 At 67 28 28 26 Aum 140 29 29 29 J@ed 125 30 30 72 J@u 234 31 31 39 Jm 235 32 32 5 Kb 50 33 33 65 Kc 124 34 34 68 Kd 77 35 35 38 Kev 120 36 36 92 Kf 144 37 37 13 Kgd 75 38 38 122 Kk 208 39 39 7 Kl 79 40 40 11 Kll 82 41 41 4 Klm 81 42 42 9 Klu 80 43 43 71 Kmo 145 44 44 114 Kmt 164 45 45 1 Ks 49 46 46 32 Ktc 122 47 47 10 Ku 242 48 48 88 MDtj 250 49 49 5 Mbs 247 50 50 41 Ml 252 51 51 58 Mm 248 52 52 38 Mmc 240 53 53 16 O_rm 257 54 54 7 PMu 244 55 55 94 Ps 245 56 56 25 QTbf 62 57 57 92 Qal 1 58 58 44 Qcl 2 59 59 3 Qd 16 60 60 15 Qf 4 61 61 5 Qfc 10 62 62 54 Qg 218 63 63 15 Qgc 3 64 64 236 Ql 11 65 65 69 Qr 7 66 66 1 Qs 11 67 67 142 Qt 9 68 68 103 Qti 37 69 69 4 TKf 30 70 70 11 TKg 45 71 71 5 Tai 22 72 72 10 Tam 21 73 73 39 Tas 20 74 74 2 Tc 25 75 75 10 Tg 48 76 76 78 Tht 18 77 77 12 Ti 34 78 78 10 Tl 14 79 79 2 Tls 64 80 80 17 Ts 12 81 81 13 Tv 24 82 82 1 Tvd 23 83 83 4 Tvr 6 84 84 6 Tvt 41 85 85 18 Tvv 24 86 86 87 _m 228 87 87 18 _mi 263 88 88 15 _rp 115 89 89 14 _u 262 90 90 78 _wf 266 91 91 94 water 216 ******************************************************************************** AAT Item Definitions: LINE_TYPE is a character item defining the geologic line type LINE_CODE is an integer item defining a numerical code which directly correlates to LINE_TYPE LINE_SYM is an integer item defining the cartographic line style from the lineset alcwrg.lin **************************ennisgeo.aat****************************************** COLUMN ITEM NAME WIDTH OUTPUT TYPE N.DEC ALTERNATE NAME INDEXED? 1 FNODE# 4 5 B - - 5 TNODE# 4 5 B - - 9 LPOLY# 4 5 B - - 13 RPOLY# 4 5 B - - 17 LENGTH 8 18 F 5 - 25 ENNISGEO# 4 5 B - - 29 ENNISGEO-ID 4 5 B - - 33 LINE_TYPE 25 25 C - - 58 LINE_CODE 3 3 I - - 61 LINE_SYM 3 3 I - - Record CASE# FREQUENCY LINE_CODE LINE_TYPE LINE_SYM 1 1 6917 1 certain contact 25 2 2 320 2 approximate contact 26 3 3 326 4 certain fault 1 4 4 1 5 approximate fault 3 5 5 873 7 certain normal fault 1 6 6 12 8 approximate normal fault 3 7 7 170 10 certain reverse fault 1 8 8 4 11 approximate reverse fault 3 9 9 621 13 certain thrust fault 1 10 10 3 14 approximate thrust fault 3 11 11 6 16 detachment fault 3 12 12 219 30 dacite sill (Kd) 1 13 13 82 40 diabase dike (!di) 1 14 14 1 60 marble (Ama) 1 15 15 218 90 water contact 25 16 16 337 99 map boundary 1 ******************************************************************************** -------------------------------------------------------------------------------- ENNISFLT: Arc coverage containing all structure lines including faults and folds. AAT Item Definitions: LINE_TYPE is a character item defining the geologic line type LINE_CODE is an integer item defining a numerical code which directly correlates to LINE_TYPE LINE_SYM is an integer item defining the cartographic line style from the lineset alcwrg.lin **************************ennisflt.aat****************************************** COLUMN ITEM NAME WIDTH OUTPUT TYPE N.DEC ALTERNATE NAME INDEXED? 1 FNODE# 4 5 B - - 5 TNODE# 4 5 B - - 9 LPOLY# 4 5 B - - 13 RPOLY# 4 5 B - - 17 LENGTH 8 18 F 5 - 25 ENNISFLT# 4 5 B - - 29 ENNISFLT-ID 4 5 B - - 33 LINE_TYPE 25 25 C - - 58 LINE_CODE 3 3 I - - 61 LINE_SYM 3 3 I - - Record CASE# FREQUENCY LINE_CODE LINE_TYPE LINE_SYM 1 1 60 3 concealed contact 43 2 2 326 4 certain fault 1 3 3 1 5 approximate fault 3 4 4 6 6 concealed fault 44 5 5 873 7 certain normal fault 1 6 6 12 8 approximate normal fault 3 7 7 45 9 concealed normal fault 44 8 8 170 10 certain reverse fault 1 9 9 4 11 approximate reverse fault 3 10 10 35 12 concealed reverse fault 44 11 11 619 13 certain thrust fault 1 12 12 3 14 approximate thrust fault 3 13 13 60 15 concealed thrust fault 44 14 14 6 16 detachment fault 3 15 15 227 20 certain fold axis 25 16 16 21 22 concealed fold axis 43 17 17 34 60 marble (Ama) 1 18 18 172 98 7.5 min tic marks 25 ******************************************************************************** -------------------------------------------------------------------------------- ENNISSYM: Arc coverage containing cartographic structural line decorations (sawteeth, bar-and-ball symbols, fold arrows). AAT Item Definitions: LINE_SYM is an integer item defining the cartographic line style from the lineset alcwrg.lin **************************ennissym.aat****************************************** COLUMN ITEM NAME WIDTH OUTPUT TYPE N.DEC ALTERNATE NAME INDEXED? 1 FNODE# 4 5 B - - 5 TNODE# 4 5 B - - 9 LPOLY# 4 5 B - - 13 RPOLY# 4 5 B - - 17 LENGTH 8 18 F 5 - 25 ENNISSYM# 4 5 B - - 29 ENNISSYM-ID 4 5 B - - 33 LINE_SYM 3 3 I - - Record CASE# FREQUENCY LINE_SYM 1 1 4528 25 ******************************************************************************** -------------------------------------------------------------------------------- ENNISATT: Arc and point coverage containing bedding and foliation attitude information in the form of cartographic strike and dip symbols (arcs) and dip values (points). PAT Item Definitions: DIP is a character item defining the dip angle in degrees (ranging from 0-90) **************************ennisatt.pat****************************************** COLUMN ITEM NAME WIDTH OUTPUT TYPE N.DEC ALTERNATE NAME INDEXED? 1 AREA 8 18 F 5 - 9 PERIMETER 8 18 F 5 - 17 ENNISATT# 4 5 B - - 21 ENNISATT-ID 4 5 B - - 25 DIP 8 8 C - - Values for DIP range from 2 to 89 ******************************************************************************** AAT Item Definitions: LINE_SYM is an integer item defining the cartographic line style from the lineset alcwrg.lin **************************ennisatt.aat****************************************** COLUMN ITEM NAME WIDTH OUTPUT TYPE N.DEC ALTERNATE NAME INDEXED? 1 FNODE# 4 5 B - - 5 TNODE# 4 5 B - - 9 LPOLY# 4 5 B - - 13 RPOLY# 4 5 B - - 17 LENGTH 8 18 F 5 - 25 ENNISATT# 4 5 B - - 29 ENNISATT-ID 4 5 B - - 33 LINE_SYM 3 3 I - - Record CASE# FREQUENCY LINE_SYM 1 1 6963 1 ******************************************************************************** --------------------------------------------------------------------------------