Glacial Geology of the Southern Uinta Mountains

Benjamin J.C. Laabs* and Eric C. Carson†

ABSTRACT

It has been known for over a century that the Uinta Mountains contained numerous alpine during parts of the Quaternary Period, yet until recently, the glacial record on the south side of the range had received little scientifi c attention. Results of recent 1:24,000-scale fi eld mapping of surfi cial deposits in the southern Uinta Mountains indicate that glaciers in the southwestern and southeastern valleys were confi ned to deep canyons during the Last Glacial Maximum, whereas large glaciers in the south-central drainage basins extended beyond the mountain front. In contrast to the abundance of small glaciers on the north slope of the range, the south slope was dominated by six larger glaciers that attained areas in excess of 150 km2 in the North Fork Duchesne, Rock Creek, Lake Fork, Yellowstone, Uinta River, and Whiterocks drainage basins. During the Last Glacial Maximum, these glaciers had maximum ice thicknesses of ~500 m. In addition, seven smaller valley glaciers (3.5 to 79.3 km2) occupied minor catchments in the southern Uinta Mountains. Latero-frontal marking the maximum advance of glaciers are best preserved below the mouths of Lake Fork, Yellowstone and Uinta canyons. These landforms provide evidence of multiple Pleistocene advances. The youngest are the Smiths Fork and Blacks Fork Glaciations, which, on the basis of cosmogenic dating and morphology of moraines, occurred during marine oxygen-isotope stages 2 and 6, respectively. An earlier (stage 16?) glacial episode, herein termed the Altonah Glaciation, is indicated by an extensive lateral beyond the mouth of Yellowstone canyon as well as moraines in Lake Fork and Uinta River canyons. At higher elevations, alpine glacial landforms, including , rock glaciers, arêtes, and hanging valleys are ubiquitous. Most glacial sediments on valley fl oors in the southern Uinta Mountains were deposited during the last deglaciation (~17.6 to 12 ka); these include moraines that may indicate a minor ice advance at ~13 ka in a south-central valley (Carson, 2003). In contrast, ice had disappeared from at least one valley in the eastern Uintas by ~14 ka (Munroe, 2002), indicating spatial variability in the responses of glaciers to latest Pleistocene climate change. Additional research aimed at identifying the time of the local Last Glacial Maximum and subsequent deglaciation in the southern Uinta Mountains is underway.

INTRODUCTION Licciardi and others, 2001; and the Rockies, Benson and others, 2004a) and adjacent The Uinta Mountains form an east-west to the eastern edge of the Lake Bonneville basin. trending range in the central Rocky Mountains, Their orientation and location provides a unique with primary drainage to the north and south in opportunity to study what may represent glacial formerly glaciated valleys (figure 1). The range advance under cold, dry conditions in the eastern is located centrally among well-dated alpine Uintas and cold, wet, pluvial conditions in glacial localities (e.g., the Wind River Mountains, western valleys that were closer to Lake Bonneville Gosse and others, 1995; the Yellowstone Plateau, (Munroe and Mickelson, 2002). Alpine glaciers

*Geology Department, Gustavus Adolphus College, St. Peter, MN 56082 Laabs, B.J.C., Carson, E.C., 2005, Glacial geology of the southern Uinta [email protected] Mountains, in Dehler, C.M., Pederson, J.L., Sprinkel, D.A., and Kowallis, †Geology Department, San Jacinto College, Houston, TX 77049 B.J., editors, Uinta Mountain geology: Geological Association Publication 33, p. 235-253.

235 Glacial Geology of the Southern Uinta Mountains B.J.C. Laabs and E.C. Carson

Figure 1. A) Inset location map of the Uinta Mountains in Utah. B) Shaded-relief map of the southern Uinta Mountains. Glaciated valleys are labeled; NFD = North Fork Duchesne, BS = Blind Stream, LH = Log Hollow, RC = Rock Creek, LF = Lake Fork, YS = Yellowstone, CC = Crow Canyon, DG = Dry Gulch, UR = Uinta River, PC = Pole Creek, WR = Whiterocks, DF = Dry Fork, SC = Split Creek. were numerous in the Uinta Mountains during the were termed the Blacks Fork and Smiths Fork Last Glacial Maximum (LGM), as documented by Glaciations by Bradley (1936), and were later Atwood (1909), Bradley (1936), Bryant (1992), correlated respectively to the Bull Lake and Munroe (2001), and surficial geologic mapping Pinedale Glaciations in the Wind River Mountains described herein. Thirteen drainage basins on by Richmond (1965) (table 1). Results of recent the south side of the Uinta range contained alpine work in the Wind River Mountains and elsewhere valley glaciers that left a well-preserved record of ice extent. However, the extent of past glaciers in Table 1. Pleistocene glaciations in the Uinta Mountains these valleys has been only broadly delimited in previous mapping efforts: accordingly, the primary Uinta Rocky Mountain Marine Approximate of objectives of this paper are to describe the Mountain Correlative Oxygen Age (ka)2 glacial geology of the southern Uinta Mountains, Glaciation Isotope Stage to provide a reconstruction of glacial extents (MIS) during the LGM, and to summarize the Quaternary Smiths Fork1 Pinedale 2 24 - 12 glacial history of the Uinta Mountains based on the Blacks Fork1 Bull Lake 6 186 - 128 mapped record. A detailed understanding of the Altonah Sacagawea Ridge3 16 659 - 620 glacial record in the Uinta Mountains will provide 1From Bradley (1936). the framework for studying glacial chronology 2From Imbrie and others (1984). See text for approximate ages and paleoclimate in this unique physiographic of glaciation. setting. 3Temporary correlation and age assignment (see Chadwick and The last two glaciations in the Uinta Mountains others, 1997). 236 Dehler, Pederson, Sprinkel, and Kowallis, editors 2005 Utah Geological Association Publication 33 in the Rocky Mountains demonstrates that these RESULTS OF GLACIAL MAPPING glacial cycles occurred during marine oxygen- isotope stage (MIS) 6 (186 to 128 ka; Imbrie and Glacial Erosional Landforms others, 1984) and MIS 2 (24 to 12 ka; Imbrie and others, 1984), respectively. Glacial maxima during U-shaped valleys resulting from broadening of MIS 6 occurred at ~160 ka in the nearby Wind River preexisting valleys by alpine glaciers are ubiquitous Mountains (Sharp and others, 2003) and at 23 to in the glaciated part of the southern Uinta Mountains 16 ka in the Wind Rivers, the Yellowstone Plateau, (fi gure 1). Glaciers in tributary valleys of major and the Colorado Rockies during MIS 2 (Gosse drainage basins coalesced and advanced into U- and others, 1995; Licciardi and others, 2004; shaped, trunk valleys. The widest U-shaped valley Benson and others, 2004b). Based on cosmogenic in the southern Uintas is in the Rock Creek drainage 10Be surface-exposure dating of moraine boulders, basin, where the horizontal distance between Laabs (2004) found that the Smiths Fork maximum trimlines on valleys sides exceeds 3 km. Whereas occurred prior to 17.6 ± 1.1 ka in the south-central streams in many glacial valleys have subsequently Uinta Mountains, which confirms the correlation smoothed their long profi les by downcutting into of the Smiths Fork and Pinedale moraines. For bedrock, some tributary streams still exhibit a the purpose of this paper, we use the correlations glacial staircase or step-down topography common of Richmond (1965); at least until direct dating of to alpine glacial valleys (fi gure 2). Blacks Fork-age deposits is established. Hanging valleys are common in the southern Uinta Mountains where tributary valleys intersect METHODS

The geomorphology of the south flank of the Uinta Mountains was mapped at the 1:24,000 scale on 25 U.S.G.S topographic maps and digital elevation models. Surficial deposits and landforms were first identified and delineated on maps and air photos. Then, glacial deposits and landforms were field checked in most accessible areas, but some features were identified only on maps and aerial photographs. Ice extents were interpreted from end moraines at the mouths of glacial valleys, by lateral moraines and trimlines on valley sides, and by breaks in slope on headwalls (i.e., the uppermost ice extent was considered to have been below the points where the slope angle on the cirque headwall exceeds 60°; Meierding, 1982). Areal extent of ice during past glaciations was calculated in a geographic information system. Maximum ice thicknesses were estimated using the differences in elevation of the lateral moraine surface and the valley floor at locations of paleo-equilibrium lines; the Figure 2. Step-down topography near the head of the latter were estimated by Shakun (2003) based North Fork Duchesne canyon. Dashed line indicates on the accumulation area ratio, toe-headwall ice extent during the last glaciation. Arrows indicate altitude ratio, lateral-moraine elevation, and former ice flow directions. Topographic map is a portion cirque-floor elevation methods. of the U.S. Geological Survey Mirror Lake 7.5-minute quadrangle.

237 Glacial Geology of the Southern Uinta Mountains B.J.C. Laabs and E.C. Carson more deeply eroded trunk valleys. Several glaciated accumulation areas of glaciers were largest and the hanging valleys in this area are very broad; for development of ice caps that drained into multiple example, Brown Duck basin is more than 12 km valleys was common. In the south-central Uintas, the wide above Lake Fork canyon (fi gure 3). Such most prominent arêtes have more than 450 m of relief valleys must have contained many small glaciers at and are more than 10 km in length. In the southeastern the onset of past glaciations that ultimately coalesced Uintas, rounded unglaciated divides locally termed before joining larger glaciers during ice advance. The “bollies” are more common than narrow arêtes. mouths of some hanging valleys are characterized by Examples of these features include broad divides that waterfalls in tributaries, whereas others have deep, separate glacial valleys in the headwaters of Dry Fork narrow, bedrock gorges probably cut by streams and Ashley Creeks (fi gure 4). A col is an area of low- of glacial meltwater during deglaciations. In the elevation at the summit (a French term for “mountain southern Uintas, the highest cascading waterfalls pass”); these are found at the heads of many valleys in below hanging valleys are ~300 m at Bluebell Creek the southern Uintas. They vary from narrow divides in Uinta River canyon and ~350 m at Atwine Creek to broad, till-mantled benches with small, lake-fi lled in Lake Fork canyon (fi gure 3). depressions (fi gure 5).

Figure 3. Brown Duck Basin, a hanging valley in Lake Fork basin. Dashed line indicates ice extent during the last glaciation. Arrows show former ice flow directions. Figure 4. Broad divides (or “bollies”) between Whiterocks Cascading waterfalls (CW) above the Lake Fork River (WR) and Dry Fork (DF) basins. Dashed lines indicate (LFR) are up to 350 m high. Topographic map is a ice extent during the last glaciation (ice extent in valleys portion of the U.S. Geological Survey 15- adjacent to WR and DF is not shown). Arrows indicate minute quadrangle. former ice-flow directions. Topographic map is a portion of the U.S. Geological Survey Dutch John 15-minute Cirques are very common at the heads of glacial valleys quadrangle. in the southern Uintas. Cirque basins are cut into sedimentary rocks of the Proterozoic Uinta Mountain Glacial Deposits Group and generally contain lakes (or tarns), some of which are dammed by moraines on their down- Most glacial deposits in the Uinta Mountains valley sides. The deepest in the southern Uinta are characterized as diamictons – unstratifi ed, Mountains is Crater Lake (35 m deep; Probst and unsorted sediment ranging in size from fi ne sand others, 2000), located in a cirque basin at the head of to large boulders. Silt and clay are not abundant Lake Fork canyon. in most glacial diamicton in the Uintas because the Arêtes and cols are most common in the south- dominant sources of this material are coarse-grained central and southwestern Uinta Mountains, where clastic sedimentary rocks of the Uinta Mountain

238 Dehler, Pederson, Sprinkel, and Kowallis, editors 2005 Utah Geological Association Publication 33 not striated and it is less compact than basal till.

Outwash

Glacial-fl uvial sand and gravel (outwash) is very common on valley fl oors downstream of moraines. Outwash deposits are most extensive south of moraines at the mouths of Lake Fork, Yellowstone, Uinta, and Whiterocks canyons (see fi gure 1 for locations), where outwash fans grade into outwash terraces. In most valleys, Smiths Fork-, Blacks Fork- and pre-Blacks Fork-age terraces are 5 to 12 m, 25 to 45 m, and up to 125 m above modern Figure 5. Broad upland at the divide between North Fork Duchesne (NFD) and Rock Creek (RC) basins. Dashed stream level, respectively. Outwash is composed lines indicate ice extent during the last glaciation; solid of unconsolidated, moderately to well-sorted, black line is the present drainage divide and approximates stratifi ed deposits of sand and gravel containing the location of the former between the basins. well-rounded sandstone and orthoquartzite clasts Arrows indicate former ice flow directions. Topographic and Paleozoic limestone locally. Sand lenses and map is a portion of the U.S. Geological Survey Kings Peak clast-supported gravel bodies are common, with 15-minute quadrangle. coarser-grained bodies more commonly found at the heads of outwash fans. Clasts are locally coated with Group (although shales are present in the Uinta secondary carbonate in older outwash deposits and Mountain Group). Diamictons deposited by trunk in deposits rich in primary carbonate derived from valley glaciers are generally matrix supported with Paleozoic sedimentary rocks. 20 to 50% clasts, and tend to be coarser-grained Nelson and Osborn (1991) also mapped outwash at high elevations where the transport distance by deposits over a broad area of the piedmont south of ice was less. The dominant clast size is highly the Uinta Mountains in the Uinta Basin, whereas our variable and dependent on the source rock in the mapping focused on deposits in the vicinity of glacial Uinta Mountain Group. Cobbles and boulders of termini. They provide a more detailed description of sandstone and orthoquartzite of the Uinta Mountain outwash terraces and correlated several Pleistocene Group are the dominant clasts in glacial diamicton terraces across the south-central Uintas and assigned in the southern Uinta Mountains except in the Log ages to terraces based on soil-development indices. Hollow and Blind Stream basins (see fi gure 1), where cobbles of Paleozoic sedimentary rocks are MORAINE SEQUENCES IN THE dominant. SOUTHERN UINTA MOUNTAINS Diamicton deposited directly by glacier ice is called till. Basal and supraglacial till were identifi ed Moraine ridges deposited during the past two or in the southern Uinta Mountains. These are more glaciations are well preserved in several glacial distinguished by differences in their sedimentary valleys in the southern Uintas. Narrow, latero- properties, their relative degree of compaction, and frontal moraines are common at the mouths of the the types of landforms they comprise. Basal till is largest glacial valleys as ridges up to 80 m high and composed of sandy diamicton with 20 to 40% clasts >11 km long. Stagnant-ice deposits are found at ranging in size from pebbles to small boulders. Clast the mouths of smaller canyons where ice deposited size generally decreases downvalley, and clasts are broad areas of hummocky topography. Small, generally subangular or subrounded with striated low-relief recessional moraines are located up- surfaces. Supraglacial diamicton is much more valley from prominent terminal moraines and were variable in texture. Its grain-size distribution can deposited during overall glacier retreat. This section be very similar to basal till, but it generally contains describes the moraine record in the southern Uinta a greater abundance of large, angular clasts that are Mountains, focusing on the Lake Fork, Yellowstone, 239 Glacial Geology of the Southern Uinta Mountains B.J.C. Laabs and E.C. Carson and Uinta Canyons where moraine sequences are Moraines in the Southwestern best preserved. Uinta Mountains

Geomorphic Criteria for Distinguishing During the Smiths Fork Glaciation, large glaciers Moraines of Different Ages occupied valleys in the North Fork Duchesne River (NFD on fi gure 6A) and Rock Creek (RC on fi gure 6A) Multiple moraine ridges were mapped at the canyons and attained respective areal extents of 148 mouths of several glacial valleys. At the mouth of each and 289 km2 and volumes of 22 and 46 km3 (Shakun, valley, the innermost, prominent end moraines were 2003). Only the Rock Creek glacier extended mapped as Smiths Fork, and were likely deposited at beyond the mountain front (fi gure 6A). Both glaciers (or, in some cases, shortly after) the LGM (22 to 18 deposited abundant till throughout their drainage ka). In the Lake Fork and Yellowstone canyons, this basins (especially during ice retreat), but landsliding assumption is corroborated by new 10Be cosmogenic and other erosional processes in the lower parts of exposure dates in Laabs (2004). A weighted mean these valleys have removed some lateral moraines and age of 13 moraine boulders at the crests of Smiths parts of end moraines. Headwaters of these drainages Fork-age terminal moraines in each of these two are broad valleys that contained extensive ice fi elds canyons indicate that the moraines were deposited during glaciations (fi gure 6A). The two glaciers just prior to 17.6 ± 1.1 ka. were also fed by an in the eastern North Fork Older moraines down valley from Smiths Fork- Duchesne and western Rock Creek basins (fi gure 5). age moraines are more diffi cult to date because, Glaciers in these two valleys deposited moraines at despite morphological differences, they can exhibit their termini, but only fragments of these landforms soil-developmental characteristics similar to Smiths remain in the landscape. In the North Fork Duchesne Fork-age moraines (Osborn, 1973; Douglass, canyon, two fragmented, low-relief moraines are 2000). Furthermore, most of these moraines are present at the mountain front (fi gure 6B). The outer located on Ute Tribal land and can only be studied Blacks Fork-age moraine has a rounded crest, few remotely. In places, the outer moraines are separated boulders at its surface, and appears to be eroded in from Smiths Fork-age moraines by prominent ice- places whereas the inner, Smiths Fork-age moraine is marginal drainage valleys (up to 60 m deep), higher, has a narrower crest and is more continuous. suggesting that they were deposited during a glacial Beyond the mouth of the Rock Creek canyon, a cycle that predates the LGM. In addition, some sequence of left-lateral and end moraines marks the outer moraines physically grade to an lowermost extent of ice during the last two glaciations that is much higher in the landscape than Smiths (fi gure 6C). The Smiths Fork-age moraines have Fork-age outwash. These outer moraines are herein narrower ridge crests and locally control modern correlated to either the type Blacks Fork moraine in drainage, whereas the Blacks Fork-age moraines are the northern Uintas (186 to 128 ka; table 1) or the broader, eroded in places, and are commonly dissected type Altonah moraines at the mouth of Yellowstone by small streams. The multiple Smiths Fork-age end canyon (>186 ka) (Bradley, 1936; Munroe 2001). moraines found within Rock Creek canyon likely mark Additional work is necessary to accurately determine glacier termini during brief stillstands that occurred as the ages of pre-Smiths Fork-age moraines. ice retreated from its LGM position. Moraines and other glacial deposits up-valley Despite the abundance of till in the upper parts from Smiths Fork-age moraines were likely deposited of the North Fork Duchesne and Rock Creek basins by glacial stillstands or minor readvances near (fi gure 6A), few moraines are found in these areas. the end of the Smiths Fork Glaciation, possibly in In general, the surfi cial geology on valley fl oors is response to the Younger Dryas cooling event. Small, characterized by thin till (<4 m thick) over bedrock. low-relief cirque moraines may have been deposited This may indicate rapid glacial retreat following the by cirque glaciers during the Holocene, similar to a Smiths Fork maximum. Only one cirque moraine high-elevation moraine in the northern Uintas (e.g., exists below an unnamed lake at the head of the Rock Munroe, this volume). Creek basin (fi gure 6A). Relatively small glaciers advanced in the Blind

240 Dehler, Pederson, Sprinkel, and Kowallis, editors 2005 Utah Geological Association Publication 33

Figure 6. (A) Mapped glacial deposits superimposed on shaded relief in the southwestern Uintas. (B) Glacial geology at the mouths of North Fork Duchesne (NFD) canyon and (C) Rock Creek (RC) canyon. Boxes indicate areas shown in Figure 6B and C. Topographic maps are portions of the Kings Peak and Duchesne 15-minute quadrangles (B) and the 7.5-minute Hanna quadrangle (C). North is up on all figures. See figure 1 caption for explanation of abbreviations.

Stream (BS on fi gure 6A) and Log Hollow (LH on heads and advanced beyond the mountain front, fi gure 6A) basins and attained respective areal extents depositing the best-preserved sequences of latero- of 16 and 8 km2 during the LGM. Both glaciers frontal moraines in the southern Uinta Mountains deposited abundant till throughout their basins; (fi gure 7A). The glacial record in each of these however, due to widespread landsliding in the Blind basins includes moraines from three glaciations; Stream basin, only fragments of moraine ridges are the Smiths Fork and Blacks Fork Glaciations are preserved, whereas moraines in Log Hollow are well represented along with the older Altonah Glaciation. preserved throughout the basin (fi gure 6A). Details Well preserved outwash fans and terraces have clear on the glacial geology of these two basins are in Laabs relationships with terminal moraines from three (2004). glaciations and have heights up to 125 m above modern stream level. Moraines in the South-Central Uinta Mountains Lake Fork Canyon In Lake Fork canyon, the wide valley mouth is Valley glaciers fi lled the Lake Fork (LF in fi gure split by a bedrock knob in its center. The Lake Fork 7A), Yellowstone (YS in fi gure 7A), and Uinta River River fl ows on the east side of this knob, allowing for (UR in fi gure 7A) canyons during middle and late excellent preservation of moraines on the western Quaternary glaciations. In each of these basins, large side of the valley (fi gure 7B). Terminal moraines glaciers coalesced from broad ice fi elds at the valley 241 Glacial Geology of the Southern Uinta Mountains B.J.C. Laabs and E.C. Carson

Figure 7. Map of glacial deposits in the south-central Uintas superimposed on shaded relief. (B) Enlargement of glacial geology at the mouths of Lake Fork, (C) Yellowstone, and (D) Uinta River canyons. Boxes indicate areas shown in Figures 7B, C, and D. Topographic maps are portions of the U.S. Geological Survey Kings Peak and Duchesne 15-minute quadrangles (north is up on all maps). White dots are locations of prominent peaks described in the text; ML = Mt. Lovenia; KP = Kings Peak; ME = Mt. Emmons. See fi gure 1 caption for explanation of abbreviations.

242 Dehler, Pederson, Sprinkel, and Kowallis, editors 2005 Utah Geological Association Publication 33 are separated by narrow, continuous ice-marginal split into two distinct units. The Altonah I moraine drainage valleys up to 60 m deep. Smiths Fork and is a broad, eroded, low-relief ridge whereas the Blacks Fork-age moraines are compound in places, Altonah II moraine is a narrow, continuous ridge in which individual ridges have narrow crests with with up to ~90 m of relief and appears to be eroded up to 50 m of relief (Smiths Fork-age moraines at the surface and on hillslopes. The soil in this generally have greater heights). An outwash fan moraine exhibits stage-III carbonate development, originates from the distal edge of the Smiths Fork suggesting that it may be middle-Pleistocene in moraine and grades into a terrace that is 5 to 12 age (Nelson and Osborn, 1991). This is consistent m above the Lake Fork River (fi gure 7B). Another with a correlation of this moraine to the Sacagawea outwash fan originates from the Blacks Fork moraine moraine in the Wind River Mountains (Chadwick and grades into a much higher terrace that is >20 and others, 1997). m above the Smiths Fork-age terrace. Recessional An extensive sequence of recessional moraines moraines are numerous in Lake Fork canyon and and terraces is located on the sides of delimit ice margins during overall retreat near the Yellowstone canyon up-valley from the Smiths end of the last glaciation. Most notable of these is Fork . These features mark the a 5-m-high, continuous latero-frontal moraine that dams the south end of Twin Pots Reservoir (fi gure 7B). The outer, Altonah-age moraines are broad, up to ~50 m high, and appear to be more eroded and dissected by gullies than the Blacks Fork- and Smiths Fork-age moraines. The outwash terrace extending from the Altonah-age moraines is >20 m above the Blacks Fork-age outwash terrace and ~50 m above modern grade.

Yellowstone Canyon

Moraines at the mouth of Yellowstone canyon are also well preserved, and a sequence of lateral moraines separated by deep, ice-marginal drainage valleys is most prominent (fi gure 7C). The Smiths Fork moraines have >70 m of relief and form the most extensive latero-frontal ridge in the sequence (fi gure 8A). The outwash terrace that originates at the outermost Smiths Fork moraine is 5 to 12 m above the Lake Fork River (below the confl uence of the Yellowstone and Lake Fork). Blacks Fork moraines at the mouth of Yellowstone canyon have broader and more rounded crests and up to ~60 m of relief; an outwash terrace that originates Figure 8. Moraines in the south-central Uinta Mountains. A) Southward view of a sequence of lateral moraines from the end moraine is 15 to 20 m higher than deposited during the Smiths Fork (SF) and Blacks Fork the Smiths Fork-age terrace (fi gure 7B). Between (BF) Glaciations. Low-relief ridges in the foreground are the Yellowstone and Lake Fork valleys, a broad area Smiths Fork recessional moraines (SFR) and fl at surfaces of hummocky topography was deposited likely on the valley bottom are outwash deposits. B) An area of during the Blacks Fork Glaciation while glaciers hummocky topography (indicated by boxed area) deposited in each of these valleys attained maxima on the at the mountain front by glaciers in the Lake Fork (LF) piedmont (fi gure 8B). Moraines in Yellowstone and Yellowstone (YS) drainages during the Blacks Fork. valley that represent the Altonah Glaciation are Flat surfaces on the valley bottom are outwash deposits. 243 Glacial Geology of the Southern Uinta Mountains B.J.C. Laabs and E.C. Carson position of the glacier margin as it retreated after Crow Canyon and Dry Gulch 17.6 ± 1.1 ka (Laabs, 2004). The moraines have <6 m of relief, are fragmented, and are breached in Two glaciers fi lled small valleys carved into a broad places by modern stream channels (see fi gure 9). upland between Yellowstone and Uinta River canyons Kame terraces represent deposition of moderately during the past two glaciations (fi gure 7A). The larger to poorly sorted silty sand and gravel in water of these two glaciers occupied Crow Canyon (CC on fl owing between the lateral moraine or ice margin fi gure 7A), where ice advanced approximately 11 km and the valley side. They are distinguished from from a broad cirque during the Smiths Fork Glaciation. fl uvial terraces by their association with lateral Smiths Fork-age lateral moraines on the valley sides moraines and their steep gradients that mimic give way to a broad (1.5 km wide) area of hummocky former slope of the ice-surface rather than gentler topography and abundant, small lakes. This stream gradients. area is divided into Smiths Fork and Blacks Fork-age Three cirque moraines are found near the head of deposits based on morphological differences, where Yellowstone basin (fi gure 7A); the most prominent younger deposits have higher internal relief and more of these is a broad, hummocky ridge that dams abundant lakes. North Star Lake. Another broad, discontinuous, The Dry Gulch glacier deposited a sequence of bouldery right-lateral moraine dams Doll Lake. The narrow-crested moraine ridges with up to 60 m of third is a low-relief, bouldery, narrow ridge located relief. The outermost moraine was likely deposited a few km west of Kings Peak. during the Smiths Fork maximum and inner moraines were deposited during overall retreat. The Uinta River Canyon end moraine labeled “DG2” in fi gure 10 has been breached at its down-valley end. Radiocarbon dating A moraine sequence similar to those described of wood deposited during the failure indicates that the above is found at the mouth of the Uinta River moraine was likely breached in the past 90 ± 40 years canyon (fi gure 7D). In this area, lateral moraines (E. Carson, unpublished data). Subsequent incision of are well preserved, but end moraines have been sediments deposited in standing water behind moraine eroded by the Uinta River, which drains the second DG2 revealed a record that has provided limiting ages largest basin in the southern Uintas (after Rock on the timing of deglaciation in this drainage basin. Creek basin). The most extensive moraines at the Radiocarbon dating of buried terrestrial and aquatic mouth of Uinta River canyon are up to 120 m high vegetation along with preliminary diatom analyses and are interpreted to represent deposition during of samples from these sediments indicate that it was the Blacks Fork Glaciation based on the height of an an open-water pond from deglaciation through the associated outwash terrace >24 m above the Uinta middle Holocene (Carson, 2003). A calendar-year- River. Finally, the outermost moraine on the west corrected radiocarbon age for the moraine of 12.9 side of Uinta River canyon is a broad area of low-relief ± 0.7 ka limits the age of moraines DG2 and DG3 hummocky topography separated from the Blacks (fi gure 10), where DG2 must be older and DG3 Fork-age moraine by a 50-m-deep ice-marginal younger than this age. Indeed, DG3 may have been drainage valley; we interpret this feature to represent deposited by a glacier advance in response to the deposition during the Altonah Glaciation. Younger Dryas cooling episode (12.8 – 11.5 ka; Alley At least three cirque moraines are found in and others, 1993). Evidence of a glacial response to the upper part of the Uinta River basin; the most this event has not been identifi ed elsewhere in the prominent of these are near (fi gure Uinta Mountains, and deglaciation of Dry Gulch 7A). A low-relief, rounded moraine ridge is located signifi cantly post-dates deglaciation from cirque fl oor below Oke Doke Lake east of Mount Emmons and moraines ~40 km to the east. Munroe (2001) provides a double-crested, hummocky moraine is found in a a limiting calendar-year-corrected radiocarbon age cirque south of Mount Emmons. As in other basins, of >14.5 ka for Ashley Creek, more than 1500 years these moraines were likely deposited during overall older than Dry Gulch despite being ~300 m higher retreat at the end of the Smiths Fork Glaciation. than the DG2 moraine.

244 Dehler, Pederson, Sprinkel, and Kowallis, editors 2005 Utah Geological Association Publication 33

Figure 9. Right-lateral recessional moraines near the mouth of Yellowstone canyon. Black dashed lines mark ridge crests. Former ice-flow direction was right to left. Arrow points to the outermost Smiths Fork-age moraine. The Southeastern Uinta Mountains

Discrete valley glaciers occupied valleys in the southeastern part of the glaciated Uintas during Quaternary glaciations (fi gure 11A). The largest glacier in this area was in the Whiterocks (WR in fi gure 11A) basin, where ice fi elds fi lled broad headwater valleys and coalesced before advancing beyond the mountain front. The composite moraine at the mouth of Whiterocks canyon has been eroded by the Whiterocks River and may have been partially removed by mass wasting. Only right-lateral moraines of the Blacks Fork and Smiths Fork Glaciations are preserved (fi gure 11A). Glaciers in the Dry Fork (DF in fi gure 11A), Pole Creek (PC in fi gure 11A) and Figure 10. A) Sequence of Smiths Fork-age moraines in Dry Gulch (DG) basin. DG1 = darkest gray, DG2 = Split Creek (SC in fi gure 11A) valleys were smaller medium gray, DG3 = lightest gray. Solid line shows the and confi ned in canyons. End moraines deposited location of cross-section in figure 9B. Topographic map is in these valleys during the last glaciation are small a portion of the U.S. Geological Survey Heller Lake and but well preserved. Burnt Mill Spring 7.5-minute quadrangles. B) Schematic The Smiths Fork-age moraine at the mouth of cross section of moraines DG2 and DG3. See text for Whiterocks canyon is a composite ridge with up to explanation of the limiting radiocarbon age of moraines 60 m of relief (fi gure 11B). Individual ridges are DG2 and DG3. discontinuous and have either sharp or rounded ridges are up to 4 m high, and are composed mainly crests with abundant small boulders at their surfaces. of large, angular boulders. Small cirque moraines are The lowest part of this moraine is below 2075 m found below Chepeta and Taylor Lakes (fi gure 12). asl, the lowest elevation attained by Smiths Fork-age A sequence of end moraines deposited during the moraines in the southern Uinta Mountains. A broad last glaciation are confi ned to the Dry Fork canyon; outwash fan originates at this moraine and grades outwash extends eastward from these moraines and into a terrace that is <12 m above the Whiterocks forms a terrace that is generally <5 m above the Dry River near the moraine and ~5 m above the river Fork Creek. Broad lateral moraines mark the outer downstream. The outermost moraine in this area edge of the Dry Fork glacier where it overtopped is a composite ridge that was most likely deposited the canyon at Hen Lee Bench and Horseshoe Park. during the Blacks Fork Glaciation. A sequence of These moraines have hummocky surfaces and many recessional, lateral moraines is preserved in the kettle lakes, the largest of which is Dead Lake near northeast part of Whiterocks basin (fi gure 11). These Paradise Reservoir. A large landslide in lower Dry

245 Glacial Geology of the Southern Uinta Mountains B.J.C. Laabs and E.C. Carson

Figure 11. A) Map of glacial deposits superimposed on shaded relief in the southeastern Uintas. B) Enlarged map of glacial geology at the mouths of Whiterocks canyon and (C) Dry Fork canyon. Boxes indicate areas shown in figure 10B and C. Topographic maps are portions of the Dutch John 15-minute quadrangle. North is up on all maps. See figure 1 caption for explanations of abbreviations.

Fork canyon occurred in 1997 and removed part of a Smiths Fork lateral moraine. This landslide occurred during spring snowmelt and may have been related to saturation of glacial till and underlying sediment by subsurface seepage from an irrigation canal, part of which was constructed in an ice-marginal drainage channel (fi gure 13).

Comparison with Previous Mapping

In the earliest report on the glacial geology of the Uinta Mountains, Atwood (1909) noted that moraine sequences in the southern Uintas represented deposition during two glaciations, which he termed “earlier” and “later epochs” (Atwood, 1909). His map Figure 12. Cirque moraine impounding Taylor Lake shows moraines of the “earlier epoch” extending beyond (a tarn) in the headwaters of the Whiterocks basin. Former ice-flow direction was from right to left. Photo the mountain front in most areas and moraines of the by J. Munroe.

246 Dehler, Pederson, Sprinkel, and Kowallis, editors 2005 Utah Geological Association Publication 33 “later epoch” confi ned within mountain valleys. Our DISCUSSION – THE PATTERN OF mapping results differ in that we believe ice extent in GLACIATION most valleys was similar during the past two glaciations based on the relative ages of moraines at the mouths During the LGM, glaciers covered ~1460 km2 of glacial canyons (see fi gures 6, 7, and 10). Atwood in the southern Uinta Mountains, with the largest (1909) mapped several moraines confi ned to canyons glaciers advancing in the central part of the glaciated in the southern Uinta Mountains that were either not area (table 2; plate 1 - on cd only). Ice caps that identifi ed in this study or were mapped as recessional fed adjacent glaciers were largest between North moraines of the Smiths Fork Glaciation. Fork Duchesne and Rock Creek glaciers, but were Osborn (1973) mapped moraine sequences in relatively small or absent elsewhere. Interestingly, Yellowstone, Crow Canyon, Dry Gulch, and Uinta River the total area of ice cover was ~500 km2 greater in basins, subdividing moraines on the basis of morphology the southern Uintas than in the northern Uintas, and relative soil development. He documented evidence and glaciers in Rock Creek and Uinta River canyons for 8 Pleistocene glacial advances; 3 pre-Blacks Fork in were larger than any glacier in the northern Uintas age, 2 Blacks Fork or early Smiths Fork, and 3 Smiths (Munroe, 2001; fi gure 14; explanations for this Fork in age. Our age designations generally agree unexpected result are offered below). The thickest with those of Osborn (1973); however, we argue that glaciers were in the western Uintas, where broad ice Smiths Fork recessional moraines do not necessarily fi elds drained into the North Fork Duchesne and justify designation as separate glacial advances, but Rock Creek canyons. The widest glacier was in could instead represent brief glacial stillstands or minor Dry Fork valley where ice overtopped the shallow oscillations during overall retreat. For Smiths Fork-age canyon and deposited hummocky, lateral moraines. moraines, this is supported by cosmogenic 10Be boulder- Equilibrium-line altitudes (ELAs) generally exposure ages that also corroborate our interpretation rose from west to east during the LGM, likely that the inner moraine at the mountain front is Smiths due to enhanced winter precipitation in western Fork in age (~17.6 ka; Laabs, 2004). valleys compared to those in the east (Munroe and Mickelson, 2002; Shakun, 2003; table 2). The east-

Table 2. Properties of reconstructed glaciers in the southern Uinta Mountains. Mean Max Mean Max Accum. Perimeter Length Area High Low Thickness Thickness Width Width ELA2 Area Glacier (km) (km) (km1) (m asl) (m asl) (m) (m) (m) (m) (m asl) (km1) N.F. Duchesne (NFD) 153.0 33.4 153.5 3580 2159 286 494 1687 2825 2920 111.9 Blind Stream (BS) 34.2 11.7 21.6 3367 2297 120 182 1015 2697 2950 17.4 Log Hollow (LH) 25.7 9.1 8.0 3311 2573 40 78 838 1047 2970 4.7 Rock Creek (RC) 237.4 42.8 288.7 359.5 2132 286 495 2390 3474 3010 223.2 Lake Fork (LF) 206.9 35.7 231.9 3692 2256 278 434 2490 3497 3040 173.4 Yellowstone (YS) 190.9 41.3 213.5 3807 2264 255 391 2585 3360 3070 151.9 Crow Canyon (CC) 29.4 11.8 17.7 3538 2756 91 194 1275 1785 3090 9.7 Dry Gulch (DG) 19.8 8.5 7.6 3341 2732 38 54 928 1047 3040 4.0 Uinta (UR) 264.0 43.0 256.8 3852 2201 281 431 2250 3099 3100 204.1 Pole Creek (PC) 25.7 10.5 18.4 3428 2785 81 133 1357 3127 3070 12.9 Whiterocks (WR) 149.9 35.9 161.5 3651 2098 229 321 1906 4070 3090 122.4 Dry Fork (DF) 80.9 22.5 79.3 3467 2488 183 283 1657 4185 3060 62.5 Spit Creek (SC) 9.2 4 3.5 3343 3000 39 66 897 992 3120 1.5 Mean 109.8 23.9 112.5 3536 2442 170 274 1637 2708 3041 85 Stand. Dev. 93.5 15.1 108.6 180 299 104 – 641 – 62 83 2From Shakun, 2003

247 Glacial Geology of the Southern Uinta Mountains B.J.C. Laabs and E.C. Carson west ELA gradient across the southern Uintas is basins. Gently dipping bedrock at the domal center steeper than the regional gradient across the western of the Uinta Mountain Arch (fi gure 14) may also United States from the Cascades to the Colorado explain why greater surface areas of such tributaries Rockies (e.g., Pierce, 2004). This may refl ect the are above LGM ELAs than in the northern Uintas, importance of Lake Bonneville as a moisture source thereby increasing the size of accumulation areas for glaciers in the western Uintas (Munroe and (and ultimately the size of glaciers) in the southern Mickelson, 2002; Munroe, this volume). Uintas. Although differences in local climate in the Reconstructions of the Smiths Fork glaciation Uintas may also explain the pattern of glaciation, it indicate that the largest glaciers were in the south- seems likely that bedrock structure and its effect on central Uintas (fi gure 14). One explanation for valley-fl oor elevations in the Uintas may have been this phenomenon is that accumulation areas were a major infl uence. simply larger in this part of the range. Indeed, the Bedrock also infl uenced the style of glacial highest part of the Uintas is in the south-central deposition in other valleys. In most valleys, glaciers part of the glaciated area and roughly coincides with deposited narrow, high-relief latero-frontal moraines, the domal center of the Uinta Mountain anticline. but glaciers in Crow Canyon and Split Creek valleys The seven largest glaciers in the southern Uintas deposited broad, hummocky end moraines. In both surround this area and had similar hypsometries to of these small catchments, fl at uplands are covered each other (fi gure 15), where at least 65% of the by Pliocene- to Pleistocene-age gravels documented accumulation area was above the equilibrium line. by Sprinkel (2002) that are the source of abundant Thus, the sizes of their accumulation areas can mass wasting deposits elsewhere in the Uintas explain which glaciers were largest (table 2). The (Laabs, 2004). Headward erosion of this unit by the large surface area above LGM ELAs may also explain Crow Canyon glacier may have caused landsliding why the total area of ice cover in the southern Uintas of debris onto the ice surface that was transported was greater than in the north (fi gure 14). Atwood to the zone, where it would have blanketed (1909) fi rst recognized that gentler bedrock dips on ice. This may have led to deposition of a broad the south fl ank may have driven glaciers to erode area of hummocky topography rather than a narrow laterally more easily than on the north fl ank, leading end moraine. Weakly-cemented shale of the Uinta to the development of broad valleys at the heads of Mountain Group outcrops at the head of Split Creek valley, which may have similarly led to deposition of hummocky end moraines. In the Dry Fork basin, weakly-cemented Pliocene to Pleistocene-age gravels may have partly controlled the pattern of glacial advance. In most valleys in the southern Uintas, broad, U-shaped valleys were carved into Proterozoic and Paleozoic strata during glacial cycles and were only partially fi lled in by glacial or alluvial sediment between glacial maxima. The setting in lower Dry Fork canyon is different, however, in that loose, Pliocene to Pleistocene-age gravel in the canyon has persisted through Quaternary glaciations and still outcrops on the west side of the canyon. These rocks have been the source of abundant post-glacial mass wasting Figure 13. Kettled right and left-lateral moraines in the Dry Fork basin. Dashed lines indicate ice extent (including the 1997 landslide mentioned above), during the last glaciation. Solid lines are moraine crests. possibly due to oversteepening by lateral glacial Shaded area is the location of the 1997 landslide described erosion and buttressing by glacier ice. Abundant in the text. Arrow indicates former ice-flow direction. mass wasting and rapid erosion of the gravel during Topographic map is a portion of the U.S. Geological the Holocene has partly fi lled in the canyon and Survey 7.5-minute Paradise Park quadrangle. obscured the effects of glacial erosion, resulting in

248 Dehler, Pederson, Sprinkel, and Kowallis, editors 2005 Utah Geological Association Publication 33

Figure 14. Reconstructed ice extents in the northern and southern Uinta Mountains. See Figure 1 for names of drainage basins on the south flank. Dashed line indicates the drainage divide between the north and south flanks. Solid line indicates the hinge of the Uinta Arch (from Bryant, 1992). North slope ice extents are from Munroe (2001). a V-shaped canyon in lower Dry Fork (fi gure 16). history of the southern Uinta Mountains summarized Nevertheless, lateral moraines above both sides here is inferred from the characteristics and limited of the canyon indicate that it was once fi lled and chronology of deposits and landforms described overtopped by glacier ice. above. Additional dating and ongoing research by the authors and J. Munroe will improve our SUMMARY OF GLACIAL HISTORY IN understanding of latest-Pleistocene (and perhaps THE SOUTHERN UINTA MOUNTAINS Holocene) glacial extent and chronology in the southern Uinta Mountains. Quaternary deposits and landforms record the history of at least three glacial cycles in the southern The Altonah Glaciations Uinta Mountains: the Altonah, Blacks Fork, and Smiths Fork Glaciations. Moraines that represent Although the ages of these glacial cycles are these events are best preserved at the mouths of unknown, they most likely predate MIS 6 and canyons in the south-central Uinta Mountains and may correlate to the Sacagawea Ridge Glaciation were deposited by the largest alpine glaciers in the recognized by Richmond (1965). Lateral and end range. Smiths Fork moraines are found in all glacial moraines in the Lake Fork, Yellowstone, and Uinta valleys. Recessional moraines and high-elevation River drainages indicate that these basins and, glacial features were deposited at the end of this probably, all of the glacial valleys in the southern cycle, during the Younger Dryas cooling event, or Uinta Mountains west of Split Creek were occupied possibly during Holocene neoglacial advances (see by ice during this cycle. In the south-central Uintas, Munroe, this volume). The Pleistocene glacial it is clear that Altonah glaciers advanced beyond the 249 Glacial Geology of the Southern Uinta Mountains B.J.C. Laabs and E.C. Carson

North Fork Duchesne Rock Creek 4000 4000 3500 3500

3000 3000 ELA = 3010 ELA = 2920 2500 2500 Elevation (m asl) Elevation (m asl) 2000 2000 0 20 40 60 80 100 0 20 40 60 80 100 Cumulative Area (%) Cumulative Area (%)

Lake Fork Yellowstone 4000 4000 3500 3500 3000 3000 ELA = 3040 ELA = 3070 2500 2500 Elevation (m asl) Elevation (m asl) 2000 2000 0 20 40 60 80 100 0 20 40 60 80 100 Cumulative Area (%) Cumulative Area (%)

Uinta River Whiterocks 4000 3900 3500 3400 3000 ELA = 3100 2900 ELA = 3090 2500 2400 Elevation (m asl) 2000 Elevation (m asl) 1900 0 20 40 60 80 100 0 20 40 60 80 100 Cumulative Area (%) Cumulative Area (%)

Dry Fork 4000 3500

3000 ELA = 3060 2500

Elevation (m asl) 2000 0 20 40 60 80 100 Cumulative Area (%)

Figure 15. Reconstructed hypsometry of the seven largest glaciers in the southern Uintas during the Smiths Fork maximum. Solid lines are reconstructed ice-surface elevations. Dashed lines are reconstructed ELAs from Shakun (2003). See figure 1B for locations.

250 Dehler, Pederson, Sprinkel, and Kowallis, editors 2005 Utah Geological Association Publication 33 mountain front and extended the furthest down (2003) of an outwash terrace in the Wind River valley of any subsequent glaciation. Mountains suggests glaciers may have advanced in the Rocky Mountains during this time. Counts The Blacks Fork Glaciation (2005) documented evidence of a MIS 4 terrace in the Henry’s Fork River on the north slope of Evidence of the Blacks Fork Glaciation is the Uintas, but similar terraces have not yet been widespread throughout the southern Uintas, identified in the southern Uintas. though none of the Blacks Fork moraines have yet been dated. These moraines most likely correlate The Smiths Fork Glaciation with the Bull Lake Glaciation, as first noted by Richmond (1965). During the Blacks Fork Deposits from the last glaciation are the most Glaciation, ice advanced beyond the mountain widespread and best dated in the Uintas. Glaciers front and onto the piedmont in south-central reached their maxima prior to 17.6 ± 1.1 ka in valleys, but was generally confined to canyons in the Lake Fork and Yellowstone canyons (Laabs, the southwestern and southeastern catchments. 2004), and retreated shortly after this time. The most prominent features that represent this Glacial stillstands or subsequent readvances event are latero-frontal moraine loops at the occurred in several valleys, as indicated by the mouths of Lake Fork, Yellowstone, and Uinta River presence of recessional moraines in the lower canyons. parts of valleys, namely in North Fork Duchesne, Moraines representing MIS 4 (71 to 59 ka; Lake Fork, Yellowstone, and Dry Gulch basins. Imbrie and others, 1984) are not found in the The age of one such advance or stillstand is Uintas or elsewhere in the Rocky Mountains, ~12.9 ka, when a small glacier retreated from but recent mapping by Chadwick and others a recessional ridge in Dry Gulch basin. In the (1997) and numerical dating by Sharp and others eastern Uintas, however, valleys were apparently

A A' SW NE

Mosby Smiths Fork Horseshoe approximate former ice surface Park 9800 Mtn Julius diamicton Park Pliocene (?) hillslope deposits gravel 9400 Smiths Fork alluvium diamicton

Elevation (ft asl) 8800 Proterozoic bedrock A'

A

Figure 16. Schematic cross section of the geology of lower Dry Fork canyon (note: thickness of geologic units is not to scale). Dashed lines show geologic contacts, gray line shows the approximate ice surface during the Smiths Fork maximum. Hillslope deposits are mainly landslides and slumps in glacial diamicton. Inset map shows cross-section line on the U.S. Geological Survey 15-minute Vernal quadrangle. Elevations are in feet above sea level to follow U.S. Geological Survey 7.5-minute topographic maps.

251 Glacial Geology of the Southern Uinta Mountains B.J.C. Laabs and E.C. Carson ice free by ~14 ka (Munroe, 2002). These dates, alpine glaciation from southwestern Colorado: along with an eastward rise in ELAs, indicate Quaternary Science Reviews, v. 24, p. 49-65. variations in climate across the southern Uintas Bradley, W.A., 1936, Geomorphology of the north during the Smiths Fork maximum and during flank of the Uinta Mountains: U.S. Geological subsequent deglaciation that may be related to Survey Professional Paper 185-I, p. 163-169. the influence of Lake Bonneville on local climate Bryant, B., 1992, Geologic and structure maps (e.g., Munroe and Mickelson, 2002). Glaciers of the Salt Lake City 1°x 2° quadrangle, likely existed in cirques in the high Uintas as late Utah and Wyoming: U.S. Geological Survey as ~13 ka, and may have advanced in response Miscellaneous Investigations Series Map I- to the Younger Dryas cooling event and possibly 1997, 1:125,000 scale. Holocene climate changes. Carson, E.C., 2003, Fluvial responses to Holocene environmental change, Uinta Mountains, ACKNOWLEDGMENTS northeastern Utah: Madison, University of Wisconsin, Ph.D. dissertation, 482 p. Funding for this research was provided by the Chadwick, O.A., Hall, R.D., and Phillips, F.M., Geological Society of America, the Jonathan Davis 1997, Chronology of Pleistocene glacial Scholarship from the Desert Research Institute advances in the central Rocky Mountains: at the University of Nevada-Reno, D. Koerner Geological Society of America Bulletin, v. 109, at the , and the National no. 11, p. 1443-1452. Science Foundation (EAR-0345277). J. Shakun, J. Counts, R., 2005. The Quaternary Stratigraphy Munroe, D. Mickelson, M. Devito, N. Oprandy, J. of the Henrys Fork and Western Browns Park, Silverman, O. Krawciw, N. Laabs, H. Kempenich, Uinta Mountains, Utah and Wyoming: Logan, Z. Shangze, C. Rodgers, K. Refsnider, and T. Utah State University, M.S. thesis, 159 p. Westlund assisted with field studies. Reviews Douglass, D.C., 2000, Glacial history of the west by D. Mickelson, J. Munroe, D. Sprinkel and J. fork of Beaver Creek, Uinta Mountains, Utah: Pederson were extremely helpful in preparing this Madison, University of Wisconsin, M.S. thesis, paper. 64 p. Gosse, J.C., Klein, J., Evenson, E.B., Lawn, B., and REFERENCES Middleton, R., 1995, Beryllium-10 dating of the duration and retreat of the last Pinedale Alley, R.B., Meese, D.A., Shuman, C.A., Gow, A.J., glacial sequence: Science, v. 268, no. 5215, p. Taylor, K.C., Grootes, P.M., White, J.W.C., 1329-1333. 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D., and Sharma, P., 2004, Variable responses Sharp, W.D., Ludwig, K.R., Chadwick, O.A., of Western U.S. glaciers during the last Amundson, R., Glaser, L.L., 2003, Dating deglaciation: Geology, v. 32, no. 1, p. 81-84. Fluvial Terraces by 230Th/U on Pedogenic Meierding, T., 1982, Late Pleistocene glacial Carbonate, Wind River Basin, Wyoming: equilibrium-line altitudes in the Colorado Quaternary Research, v. 59, p. 139-150. Front Range - a comparison of methods: Sprinkel, D.A., 2002, Progress report geologic Quaternary Research, v. 18, p. 289-310. map of the Dutch John 30’ x 60’ quadrangle, Munroe, J., 2001, Late Quaternary history of Utah-Colorado-Wyoming (year 3 of 3): Utah the northern Uinta Mountains, Northeastern Geological Survey Open-File Report 399, Scale Utah: Madison, University of Wisconsin, Ph.D. 1:62,500, 3 plates. dissertation, 398 p. – 2002, Timing of postglacial cirque reoccupation in the northern Uinta Mountains, northeastern Utah, U.S.A.: Arctic, Antarctic and Alpine Research, v. 34, no. 1, p. 38-48. Munroe, J., and Mickelson, D., 2002, Last Glacial Maximum equilibrium-line altitudes and paleoclimate, northern Uinta Mountains, Utah, U.S.A.: Journal of , v. 48, no. 161, p. 257-266. Nelson, A.R., and Osborn, G.D., 1991, Terrace profiles and relative ages of alluvial surfaces and end moraines in the northwestern Uinta Basin, Plate 4, in Morrison, R.B., editor, Quaternary nonglacial geology; conterminous U.S.: Decade of North American Geology, v. K- 2. Osborn, G.D., 1973, Quaternary geology and geomorphology of the Uinta Basin and the south flank of the Uinta Mountains, Utah: Berkeley, University of California, Ph.D. dissertation, 266 p. Pierce, K.L., 2004, Pleistocene glaciations of the Rocky Mountains, in Rose, J., Gillespie, A.R., Porter, S.C., and Atwater, B.F., editors, The Quaternary Period in the United States: Amsterdam, Elsevier, p. 63-76. Probst, J., Probst, K., and Probst, B., 2000, High Uintas Fishing: Bountiful, Utah, Outland Publishing, 106 p. Richmond, G., 1965, Glaciation in the Rocky Mountains, in Wright, H. E. and D. G. Frey, editors, The Quaternary of the United States: Princeton, Princeton University Press, p. 217- 230. Shakun, J., 2003, Last Glacial Maximum

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