SHEET 1 of 2 Version 1.0

U.S. DEPARTMENT OF THE INTERIOR OPEN-FILE REPORT 2006-1051 U.S. GEOLOGICAL SURVEY SHEET 1 of 2 Version 1.0

PHANEROZOIC PROTEROZOIC

o o 105 00' o 106 00' 106 00' 105 o 00' o 41 00' 41o 00' 377 1,380 1,400 MAP Sherman pluton EXPLANATIONS SAND CREEK PASS CRAZY MOUNTAIN SAND CREEK PASS EATON RESERVOIR DIAMOND PEAK CHEROKEE PARK VIRGINIA DALE TABLE MOUNTAIN ROUND BUTTE DIAMOND PEAK CHEROKEE PARK VIRGINIA DALE TABLE MOUNTAIN ROUND BUTTE 81.2 CRAZY MOUNTAIN 1,380 51 PHANEROZOIC EATON RESERVOIR 1,380

Tertiary and Cretaceous intrusive rocks Tmi 40 - 20 Ma intrusive rocks TKi 80 - 40 Ma intrusive rocks 616 1,380 Phanerozoic dikes 50 Tbbi Basaltic or mafic rocks Tmi Tertiary(?) intrusions Rawah pluton 1,350 72.3 TKi Tertiary and (or) Cretaceous intrusions GLENDEVEY

Ages in millions of years (Ma) 1,689 GLENDEVEY DEADMAN SOUTH BALD MOUNTAIN RED FEATHER LAKES HAYSTACK GULCH LIVERMORE MOUNTAIN LIVERMORE BUCKEYE DEADMAN SOUTH BALD MOUNTAIN RED FEATHER LAKES HAYSTACK GULCH LIVERMORE MOUNTAIN LIVERMORE BUCKEYE (Open symbols indicate vague or inexact locations)

1,380 1,390 40Ar/39Ar ages 53.6 54 Log Cabin pluton 1,390 30 - 40 1,380 56.6 58 1,390 40 - 50 1,390 50 - 80 56 57.2 54 1,263 33.3 Rb/Sr ages 36 1,390 1,351 20 - 30 1,380 1,380 (Manhattan) 63.4 50 - 80 1,380 58.7 75.8 47.1 56.4 74.4 68.7 60.2 58 44.4 70.5 K-Ar ages N RAWAH LAKES BOSTON PEAK KINIKINIK 33.6 RUSTIC 57.9 LAPORTE WELLINGTON N BOSTON PEAK KINIKINIK RUSTIC POUDRE PARK LAPORTE WELLINGTON 57.6 BIG NARROWS 52.5 61.9 POUDRE PARK 20 - 30 RAWAH LAKES 47.5 30 - 40 56.4 40 - 50 1,720 BIG NARROWS 50 - 80 80 - 540 1,388 1,390 57.3 U/Pb ages 50 - 80 1,664 HORSETOOTH RESERVOIR Zircon Fission Track (FT) ages 1,664

20 - 30 1,458 1,664 30 - 40 40 - 50 CLARK PEAK CHAMBERS LAKE COMANCHE PEAK PINGREE PARK CRYSTAL MOUNTAIN BUCKHORN MOUNTAIN HORSETOOTH RESERVOIR FORT COLLINS 50 - 80 CHAMBERS LAKE COMANCHE PEAK PINGREE PARK CRYSTAL MOUNTAIN FORT COLLINS BUCKHORN MOUNTAIN Sphene Fission Track (FT) ages CLARK PEAK 1,664 47.8 1,451.6 30 - 40 1,534.3 1,664 1,664 40 - 50 1,546 50 - 80 80 - 540 27.7 o Apatite Fission Track (FT) ages o 40 30' 40 30' 0-20 1,312 20 - 30 30 - 40 1,401 40 - 50 28.7 GLEN HAVEN 1,464 50 - 80 1,316 DRAKE Mt. Richthofen plug 80 - 540 1,594 28.7 64.8 1,370 TRAIL RIDGE 1,726 1,386 MOUNT RICHTHOFEN FALL RIVER PASS ESTES PARK GLEN HAVEN DRAKE MASONVILLE LOVELAND MOUNT RICHTHOFEN FALL RIVER PASS TRAIL RIDGE ESTES PARK LOVELAND 1,282 MASONVILLE 57.6 55.3 1,389 62.5 1,343 Mt. Richthofen 54.5 45.4 1,349 28.2 1,419 1,664 1,3681,370 1,382 PROTEROZOIC 1,523 1,385 28.8 1,664 1,516 Mt. Cumulus 57.9 1,520 Pb/Pb ages range 48.7 Proterozoic intrusive rocks 1,419 from 1,852 to 1,973 51.1 Yp Pikes Peak Granite (approx. 1,080 Ma) 1,419 on metagraywacke 404 Yg Middle Proterozoic granitic rocks (approx. 1,400 Ma) Xg Early Proterozoic granitic rocks (approx. 1,700 Ma) 1,377 1,800 PINEWOOD LAKE 1,395 Proterozoic dikes PANORAMA PEAK GRAND LAKE PANORAMA PEAK BOWEN MOUNTAIN GRAND LAKE MCHENRYS PEAK LONGS PEAK 54.1 PINEWOOD LAKE CARTER LAKE RESERVOIR BERTHOUD BOWEN MOUNTAIN MCHENRYS PEAK LONGS PEAK BERTHOUD Yam Middle Proterozoic dikes CARTER LAKE RESERVOIR

Ages in millions of years (Ma) 1,419 24.9 53.3 50.9 49.2 (Open symbols indicate vague or inexact locations) Mt. Apiatan 45.1 47.3 1,419 51.7 40Ar/ 39Ar ages Longs Peak- 540 - 1,500 25.5 1,825 1,419 55.1 49.5 1,500 - 1,900 St. Vrain 1,419 28.4 47.5 Rb/Sr ages pluton Trail Mtn. (east) 1,419 TRAIL MOUNTAIN 62.6 540 - 1,500 53.1 64 1,500 - 1,900 1,419 SHADOW MOUNTAIN ISOLATION PEAK ALLENS PARK RAYMOND HYGIENE LONGMONT TRAIL MOUNTAIN SHADOW MOUNTAIN ISOLATION PEAK RAYMOND LYONS HYGIENE LONGMONT 46.9 LYONS 60.2 1,419 54.6 1,419 Trail Mountain K-Ar ages ALLENS PARK 67.4 Porphyry Mtn. 540 - 1,500 62.2 26.8 41 52.6 57.6 58.8 44.8 1,500 - 1,900 55.9 22.7 58.8 45.1 73.6 51.1 53 79.6 52.9 U/Pb ages 60 65.8 Burnt Mtn. 48.4 50.6 540 - 1,500 47.1 1,500 - 1,900 MONARCH LAKE Audubon-Albion 60 46.6 1,415 51 1,725 71.7 60 Grassy Mtn. Sunset Jamestown 66 1,725 GRANBY STRAWBERRY LAKE MONARCH LAKE GOLD HILL BOULDER NIWOT ERIE GRANBY STRAWBERRY LAKE BOULDER NIWOT ERIE 66 WARD 51 WARD 1,110 68 Long Gulch 1,446 GOLD HILL 1,321 Tuscarora 7 1/2' quadrangle boundary 1,414 60 48.19 46 66.2 64 67 30' x 60' quadrangle boundary 1,664 60 45.1 62.06 1,725 1,714 60 64 1,429 Caribou 65.5 Bald Mtn. 43.47 62.3 66.2 1,664 Broad spectrum of Ar/Ar ages from 1,355 to 1,379 o 40 o 00' 40 00' 1,725 58 62.6 1,664 Sm-Nd age 572 Ma on garnet and clinopyroxene 60 367 Ar/Ar on biotite from 1,371 to 1,364 59 55.1, 56.2, 58.6, 59, 60.6, 1,664 EAST PORTAL 1,672 61.8, 62, 66.6, 67.1, 73 77.1 68.2 1,176 1,444 1,713 1,375 1,220 1,725 Eldora-Bryan (north) 59 58 1,405 1,670 58 1,264 1,721 BOTTLE PASS FRASER EAST PORTAL NEDERLAND 58 TUNGSTEN ELDORADO SPRINGS LOUISVILLE LAFAYETTE BOTTLE PASS FRASER NEDERLAND TUNGSTEN LOUISVILLE LAFAYETTE 29.8 57.9 1,029 ELDORADO SPRINGS 69.95 Ma Rb/Sr 70.1 73 Ma by Pb206/U238 and 1,674 Ma Rb/Sr whole-rock ages on on Eldora stock Buckeye Mtn. Pb207/U235 on pitchblende Boulder Creek batholith and Boulder 57.9 associated rocks 68.4 66 Ma by Pb207/Pb206 on pitchblende Creek 1,725 60 67 50.8 U/PbPb/Pb ages ages 1,800-1,880 1,786, 1,724, 1,536 Eldora-Bryan (south) 147 Apex 58.1 pluton 76.7 60 1,312 79.3 58.5 96, 114, 118, 120, 175 1,664 1,550 124, 132, 138, 162 61.7 52.6 69.3 64 1,415 58 66.8 67.8 74.7 63.9 63.5 1,226 1,550 1,455 Empire BYERS PEAK (Fall River) 71.3 52.8 67.3 (includes Mad Creek) Ralston dike EMPIRE 707 63.1 1,379 BYERS PEAK BERTHOUD PASS EMPIRE CENTRAL CITY 340 BLACK HAWK GOLDEN ARVADA 1,380 GOLDEN ARVADA RALSTON BUTTES 78 76 RALSTON BUTTES BERTHOUD PASS 1,350 BLACK HAWK (Miller 305 59.3 48.8 52.7 60.1 CENTRAL CITY Rb/Sr Red Mtn. 54.6 40.5 Creek) 60 54.4 142.8 1,360 Ar/Ar on biotite from 1,370 to 1,380 23.8-28.5 66 39.4 53.7 54.9 62.5 109 64 Zircon FT 57 53.8 57.5 64 Silver Plume 1,570 20.4-29.6 37.4 59.6 56.9 149.7 64 1,571 65 57.6 54 61.8 K/Ar 62.6 77.5 57.2 56 63.94 pluton 67.8 65 52.4 26.7-33.7 61.6 63.3 58.4 55.9 84.3 59.4 98.9 115.7 60.2 40Ar/39Ar 65 65 61.6 59.7 100.8 65.8 1,728 1,728 26.95-29.9 21.7 66.8 63.1 196 66.4 1,408 Ma Rb/Sr whole-rock ages 1,442 19 19.5 48.3 47.7 53.3 62.3 263 on Silver Plume Granite - 65.2 55.6 61 1,664 Ma Rb/Sr whole rock 32.3 21.8 Lincoln Mtn. 57.6 ages on metamorphic rocks; 34.3 58.4 (Pleasant Valley) 63.94 1,422 mostly Idaho Springs Fm. 23.4 43.4 61.2 25.9 41.5 1,418 GRAYS PEAK LOVELAND PASS GRAYS PEAK GEORGETOWN IDAHO SPRINGS SQUAW PASS EVERGREEN MORRISON FORT LOGAN LOVELAND PASS IDAHO SPRINGS EVERGREEN MORRISON FORT LOGAN 42.8 Paines Mtn. SQUAW PASS (Torrey's Peak) GEORGETOWN 1,728 37 Otter Mtn. Montezuma 43 36.6 98 66.5 1,228 1,400 37.9 57.8 1,442 1,134 68.5 1,298 Swan Mtn./ 37.4 1,283 1,390 Mt. Evans Breckenridge 37.4 (Geneva Basin/Cirque) 1,410 90.2 1,448 pluton Doublehead pluton 33.3 CONIFER 39.6 39.8 39.4 KEYSTONE MONTEZUMA MOUNT EVANS 134 HARRIS PARK MERIDIAN HILL CONIFER INDIAN HILLS LITTLETON KEYSTONE MONTEZUMA MOUNT EVANS MERIDIAN HILL INDIAN HILLS LITTLETON HARRIS PARK Webster 35.5 233.1 35.1 Pass 37.5 43.1 35 1,660 Ma Rb/Sr whole-rock on granite of Mt. Rosalie, 43.5, 135 Mt. Evans batholith Lone Rock pluton 44.8 34.8 71.7 45.1 58.5 39o 30' 39o 30' 93.4 194.4 1,031 36.2, 36.6, 38.2, 134.7 76.8 38.3. 45.5, 49.1, 50.6 66 119.6 1,039 71.5 79.8 Mount Guyot plug 118.9 1,025 PINE 44 57.6 64.4 79 65.9 66.1 111.9 PLATTE CANYON (Pennsylvania Creek, east) Baker Lake and Jefferson Hill 117.1 65.2 47.1 BOREAS PASS JEFFERSON MOUNT LOGAN SHAWNEE 151.9 BAILEY PINE PLATTE CANYON KASSLER BOREAS PASS MOUNT LOGAN BAILEY KASSLER 55.1 60.5 69.5 70.6 78.9 114.1 JEFFERSON 74.2 SHAWNEE 1,060 35.5, 37.6 49.8 119.6 122.8 39.9, 69.2 56.4 115.9 104.5 59.6 41.1 51 70.8 (Boreas Mtn) 115.7 36.4 149.9 1,060 155.8 130.9 Montgomery Gulch, north WINDY PEAK (South Tarryall Creek) OBSERVATORY ROCK 40.3, 40.6, 40.7, 43.2 MILLIGAN LAKES 1,060 (Little Baldy Mtn) 148 TOPAZ MOUNTAIN 1,086 COMO MILLIGAN LAKES OBSERVATORY ROCK TOPAZ MOUNTAIN WINDY PEAK GREEN MOUNTAIN DECKERS DEVILS HEAD COMO GREEN MOUNTAIN DECKERS DEVILS HEAD 60.9 124 1,308 130 63.3 245 Fort 41.5 Collins Kenosha (Palmer Peak) 54.7 Estes Park 1,011 59.7 pluton 57.4 1,032 66.4 Denver West 78.4 Pikes Peak batholith 55.5 Bailey (Crooked Creek) 56.3 74.9 EAGLE ROCK 1,085.6 66.5 1,093 ELKHORN FAIRPLAY EAST EAGLE ROCK FARNUM PEAK MCCURDY MOUNTAIN CHEESMAN LAKE WESTCREEK DAKAN MOUNTAIN FAIRPLAY EAST MCCURDY MOUNTAIN DAKAN MOUNTAIN WESTCREEK ELKHORN 473 FARNUM PEAK CHEESMAN LAKE 1,023 65.5 64.1 59.3 41 33.76 896 Index Map of Colorado 995 33.78 Map area shown with 352 42.2 Signal Butte 1:100,000-scale quadrangles 930 45.2 1,005 1,015 GARO HARTSEL SULPHUR MOUNTAIN GLENTIVAR TARRYALL HACKETT MOUNTAIN SIGNAL BUTTE MOUNT DECEPTION GARO HARTSEL GLENTIVAR TARRYALL1,035 MOUNT DECEPTION SULPHUR MOUNTAIN SIGNAL BUTTE 43.3

37.8 41.5 HACKETT MOUNTAIN 42.8 39o 00' 39 o 00'

SCALE 1:250 000 5 0 5 10 15 20 MILES

50 5 10 15 20 25 30 KILOMETERS

Any use of trade names is for desciptive purposes only and does not imply endorsement by the U.S. Government.

This map was produced on request, directly from ISOTOPIC AGES OF ROCKS IN THE NORTHERN FRONT RANGE, COLORADO digital files, on an electronic plotter.

For sale by U.S. Geological Survey Information Services, Box 25286, Federal Center, Denver, CO 80225; Anna B. Wilson and Bruce Bryant 1-888-ASK-USGS.

GIS files and a PDF file are available online at 2006 http://pubs.usgs.gov/of/2006/