Rangewide Glaciation in the Sierra Nevada, California

Rangewide glaciation in the Sierra Nevada, California

James G. Moore and Barry C. Moring U.S. Geological Survey, Mail Stop 910, Menlo Park, California 94025, USA

ABSTRACT a similar northward depression, but they are Many detailed studies have examined the Pleis- ~500–1000 m higher. tocene glacial history of selected regions, par- The 600-km-long Sierra Nevada under- The upper part of the glacial system was ticularly in the better-exposed east side of the went extensive Pleistocene glaciation except erosive over a broad highland area as the range. However, in this work, we attempt an for its southernmost 100 km. Presently, ~1700 evenly distributed ice in the accumulation integrated view of the late Pleistocene glaciation small glaciers and ice masses near the crest of zone moved to lower elevation. The abundant of the entire range. The limit of such glaciers the range occur above 3250 m in elevation; lake basins record this erosive action. The on both sides of the range has been compiled, these covered an area of ~50 km2 in 1972. lower part of the glacier system was largely providing data to calculate the equilibrium line Fourteen of the largest glaciers decreased by confi ned to major preexisting river canyons altitudes (ELA) for all the major glaciers. These about one half in area during the period from in which melting dominated. The average ELAs descend north at ~3 m per kilometer of 1900 to 2004. of rangewide estimates of the equilibrium latitude and are systematically higher on the east Rock glaciers, generally glacial ice cov- line altitude (ELA)—the boundary between side of the range. In this regard, they mimic the ered by 1–10 m of rockfall debris, occur in the upper snow and ice accumulation zone present-day May snowline and also the lower about the same span of the range as ice and and the lower ablation zone—of many late limit of the zone of the 7040 glacial lakes, which permanent snowfi elds. They are, on average, Pleistocene glaciers parallels, and is only formed in the late Pleistocene glacial accumula- lower by 200–300 m, apparently because of 200–300 m above, the altitude of the lower tion zone. This correspondence provides insight the insulating layer of rocky rubble that pro- limit of the lakes. Hence, the lake zone pro- into the climate during Pleistocene glaciation tects their internal ice from the sun’s heat vides a means of estimating the ELA. as well as an independent method of estimat- and from wind. ing the ELA. The principal Pleistocene glacial stages INTRODUCTION are the Sherwin (ca. 820 ka), Tahoe (170–130 DATA SETS and ca. 70 ka), Tioga (14–28 ka), and Recess The north-northwest–trending Sierra Nevada Peak (13 ka). Some 7040 glacial lakes, pro- of eastern California is 600 km long (430 km Elevations were derived from the U.S. Geo- duced primarily by quarrying from bed- north-south) and has a crestal elevation from logical Survey (USGS) 10 m National Elevation rock, were mostly exposed after recession 2000 to 4400 m. Presently, more than 1000 Data set (NED). Location (centroid) and size of of the Tioga glacial stage. The lakes largely small glaciers and permanent ice masses occur glacial lakes, permanent ice, and areas covered mark the area of primary snow accumula- near the crest of the range. They represent a by timber are from 1:24,000 scale Digital Line tion. Below the lower limit of the lakes, ice tiny part of the area covered by ice during the Graphic (DLG) analysis of USGS topographic fl owed downward into river-cut canyons, Pleisto cene glacial stages, when 490 km of the maps. A 1991 fi eld survey of ice, based in part forming major trunk glaciers within the crest and upper region of the range were glaci- on 300 aerial photographs taken by Austin zone of ablation. ated. Glaciation strongly modifi ed the topogra- Post in 1972, provided supplementary data on The range is in general a westward-tilted phy of the higher terrain, producing sharp peaks, present-day glaciers and permanent snowfi elds block upfaulted on its east side. Therefore, the steep canyons, moraines, and more than 7000 (Raub et al., 2006). main late Pleistocene trunk glaciers (Tahoe/ lakes (Figs. 1 and 2). Rangewide temperature and precipitation Tioga) west of the crest extend 25–60 km, We compiled quantitative data on the more data were acquired online from the Prism Cli- whereas those east of the crest extend only than 1000 present-day glaciers and ice masses, mate Group (2004; Daly et al., 1994). Seasonal 5–20 km. Because of higher precipitation as well as on rock glaciers, to compare with snow cover on the range is available from the northward, glacial features such as the toes present-day snowpack history and rangewide National Aeronautics and Space Administra- of existing glaciers and rock glaciers, as well temperature and precipitation trends in order tion (NASA) satellite with MODIS (MODerate- as the late season present-day snowline, all to judge conditions of climate change. These reso lution Imaging Spectroradiometer) (Hall decrease in elevation northward. Likewise, data were then compared with a new compila- et al., 2002; Dozier et al., 2008). the elevation of the lower limit of glacial lakes, tion of the extent of the ice over the entire range Three regional studies show the extent of late an indication of the zone of snow accumula- during the late Pleistocene. Some of these gla- Pleistocene glaciation: in Yosemite National tion during the late Pleistocene, decreases ciers spread out on the east piedmont slope of Park (Matthes, 1930; Alpha et al., 1987), in the about the same degree. This similarity sug- the range, but the main trunk glaciers on the drainage of the San Joaquin River (Matthes , gests that the overall climate patterns of the west side descended only part way down pre- 1960), and in Sequoia and Kings Canyon late Pleistocene, though cooler, were similar vious river canyons, which they modifi ed into National Parks (Moore and Mack, 2008). Only to those of today. The east slope glaciers show U-shaped canyons, such as Yosemite Valley. a few studies provide detailed information on

Geosphere; December 2013; v. 9; no. 6; p. 1804–1818; doi:10.1130/GES00891.1; 18 ﬁ gures. Received 21 December 2012 ♦ Revision received 8 August 2013 ♦ Accepted 26 August 2013 ♦ Published online 23 October 2013

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121°W 120°W 119°W 118°W 40°N

Legend Glacial Lake Elevation Reno >3500m 3000 - 3500m 2500 - 3000m 2000 - 2500m Lake 1500 - 2000m <1500m 39°N Tahoe

Bridgeport

38°N

* Modesto

37°N

* Fresno

Visalia *

36°N 0255075100 Kilometers Figure 1. Map of eastern California showing topography of the Sierra Nevada with glacial lakes shown by blue dots. The lakes were exposed and formed at the retreat of the ﬁ nal Tioga glacial stage. Note that the elevation of the range and the width, elevation, and density of the lake zone decrease toward the north.

Geosphere, December 2013 1805

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4500 tion in the east-central part of the range. Since Mt Mt Williamson N Palisade then, many workers have expanded on this early Whitney Mt Abbot Tree line Red Slate Mtn Range crest work, examining existing glaciers and mapping Mt Ritter and dating glacial deposits in restricted areas. Lakes Mt Mt Lyell The ﬁ rst regional map showing the general 4000 Olancha Mt Dana limits of ice age glaciation in the entire range V = 160 H is a small inset map in the 1938 edition of the

Tower Pk Geologic Map of California (Jenkins, 1938). The north half of this map (dated 1932) is cred- Highland Pk 3500 ited to E. Blackwelder, and the south half (dated Freel Pk 1937) is credited to F.E. Matthes. This map, and later small-scale maps showing the extent Castle Pk of glaciers over the entire range, indicates that Granite the range crest was largely covered by a con- Chief 3000 tinuous ice cap (Wahrhaftig and Birman, 1966).

Elevation (m) Actually, considerable areas near the crest, Sierra Butte particularly ridges and peaks, were ice free, as shown in the more detailed maps of Yosemite National Park (Alpha et al., 1987), and Sequoia 2500 and Kings Canyon National Parks (Moore and Mack, 2008). Blackwelder (1931) divided Pleistocene glaciation into four stages: McGee, Sherwin, Tahoe, and Tioga, from oldest to youngest. Vari- 2000 ous modifi cations and additions to this scheme have been made since, but these glacial stages 100 km still form the basis for modern studies. S N The fi rst radiometric constraints on the age of 1500 glacial deposits became available with K-Ar dat- 36° 37° 38° 39° 40° ing of volcanic rocks associated with moraines (Dalrymple, 1964). More recently, the technique N Latitude of surface exposure dating, which measures the accumulation of cosmogenic nuclides, princi- Figure 2. Profi le of range showing maximum elevation of the crest (with major peaks noted). pally 36Cl (Phillips et al., 2009) and 10Be (e.g., Glacial lakes (blue dots) generally occur in the snow accumulation zone of the last major Rood et al., 2011), has become a valuable tool Pleistocene glaciation, and tree line marks the upper limit of present-day forested terrain. for dating morainal material. All from U.S. Geological Survey topographic data. FEATURES OF THE RANGE

the limit of glaciation in the west slope canyons glacial stages, Tahoe and Tioga, which com- Topography north of Yosemite, because morainal depos- monly form paired deposits. In a few areas in its have largely been removed or are poorly the eastern Sierra Nevada, the older glacial The 600-km-long Sierra Nevada trends 30° preserved due to river erosion. We used topo- stages, McGee and Sherwin, are preserved well west of north and varies in width from 80 to graphic evidence to estimate the extent of many enough to permit recognition and mapping. 110 km (Fig. 1). Overall, the range is a coherent of the western trunk glaciers. physiographic block tilted west, and it is delim- Glacial moraines and rock glaciers have PREVIOUS WORK ited on much of its east slope by normal fault- been mapped during geologic studies that cover line scarps, which commonly defi ne a steep a large part of the range. Most of these maps The fi rst report on glaciation in California was eastern escarpment, contrasting with a much are included in the series of 15 min USGS geo- based on observations by the California Geo- gentler western fl ank. From its southern end at logic quadrangle maps compiled and duplicated logical Survey during fi eld work in the Yosemite the Garlock fault, the mountain crest rises north- online in the Sierra Nevada Batholith Mosaic region in 1863 (Whitney, 1865). Clarence King ward for 145 km to its highest point at Mount Project (Caudill, 2005). Moraine information reported evidence of glaciation in Yosemite dur- Whitney (4418 m) at 36.58°N latitude (Fig. 2). is also found on the half-degree quadrangle ing his 1864 mapping of Yosemite State Park Continuing north from Mount Whitney, the maps of the USGS geologic folios (1:125,000) (Whitney, 1865; King, 1871a) and claimed to crest maintains an elevation of greater than published around the beginning of the twenti- have found the fi rst active glaciers in the United 3200 m for 140 km to the Mammoth region near eth century, and on the more modern 1° × 2° States on Mount Shasta in 1870 (King, 1871b). the head of the San Joaquin River. A decrease in (1:250,000) geologic maps of the California John Muir was fi rst to report active glaciers in general elevation occurs in this region, but the Geological Survey. Many maps combine all the Sierra Nevada in 1871 on Black Mountain >3200 m crestal region continues north for an morainal material in one unit. Others separate, in the Yosemite region (Muir, 1873). Russell additional 107 km to 38.75°N latitude near the where possible, the two major late Pleistocene (1895) outlined details of Sierra Nevada glacia- head of the Stanislaus and Mokelumne Rivers.

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From there, the crest decreases for 150 km to ~2200 m at its north limit, south of the northern forks of the Feather River at 39.75°N latitude. North-trending normal faults along the east A side of the range mark the western limit of the Basin and Range Province, a region character- ized by crustal extension. The ﬁ rst major fault block east of the southern Sierra Nevada is the White-Inyo Mountain Range, which—though nearly as high—is only slightly glaciated because it lies in the rain shadow of the Sierra Nevada. East of the central Sierra Nevada, there are the slightly glaciated Sweetwater Moun- tains. East of Lake Tahoe, in the northern Sierra Nevada, there is the Carson Range, which is likewise only slightly glaciated. These three eastern outliers of the range are excluded in B this study. Major rivers have cut giant canyons on the west side of the range. These canyons and their tributaries have produced large moderate- elevation reentrants in the west slope (Fig. 1). The upper parts of these river canyons were occupied by trunk glaciers that carved giant U-shaped canyons.

Climate

Rain and snowfall increase markedly in the Sierra Nevada from south to north. Annual precipitation at the range crest is highly variable from year to year, but the 30 yr average Figure 3. Climate data for the Sierra Nevada for 1971–2000, showing is 800 mm in the south, and this increases sys- latitude range of present glaciers: (A) temperature (°C) and (B) pre- tematically to 1300 mm in the north. Likewise, cipitation (mm) (from Prism Climate Group, 2004). the 30 yr average precipitation at 2000 m elevation on the west slope increases about the same amount from south to north (Prism Climate Group, 2004; Fig. 3). This increase is appar- Snow covers much of the range in the winter During average years, snowpack width at 38°N ently caused by the overall northward concen- and spring, but the snowpack melts back in the lat is ~52 km (Fig. 6). tration of storm tracks commonly diverted from summer and fall. NASA’s satellite with MODIS An example of the growth and shrinkage of the south by the prevalence of elevated baro- provides useful images of the extent of the the snowpack is shown by the position of its metric pressure zones. The orographic effect of snowpack (Fig. 5), which begins growing in the lower limit (the snowline) during an average the high range causes heavier precipitation and winter and starts shrinking in February-March year, such as 2006. The average elevation of the lower snowline on the west slope compared to to ﬁ nally disappear in August-September. The snowline on the west slope of the range (Fig. the steep east slope (Fig. 4). extent of the snowpack varies considerably from 4A) is somewhat irregular up through Febru- The 30 yr average (1971–2000) of daily maxi- year to year, a pattern following the marked ary because of the accumulation and melting of mum and minimum temperatures at the range annual shifts in precipitation leading to droughts snow dumped by individual localized storms. crest are warmest at the south end, at 15 °C and and ﬂ oods, common in California on a roughly However, through April and May, the altitude 2 °C, respectively (Prism Climate Group, 2004; decadal scale (e.g., Swetnam, 1993). of the snowline systematically rises from 1500 Fig. 3). Proceeding north, they are both coolest The highly variable annual extent of the to 2600 m at 38°N latitude as temperatures in the middle high part of the range at 5° and snowpack can be assessed by examining its increase and the snow melts. –5 °C and then increase to 12 °C and –1 °C, width at different dates during different years In contrast, the east side snowline (Fig. 4B) is respectively, in the north. In contrast, the 30 yr (Fig. 6). The width of the snowpack during the systematically higher by roughly 500–1000 m average maximum and minimum temperatures past 11 yr as measured on 1 May along the 38th compared to that of the west. It follows a similar at 2000 m elevation decrease systematically parallel was narrowest (~40 km) during the pattern of rising through April and May, but it from 17 °C and 5 °C, respectively, in the south drought year of 2007 and widest (~70 km) dur- moves from 2400 to 3200 m (at 38°N latitude). to 14 °C and –1 °C, respectively, in the north. ing the exceptionally heavy snow year of 2011. The base of the snowpack on both west and Present-day ice occurs along the range crest, This nearly twofold increase in snowpack width east sides tilts down to the north at midseason where the 30 yr average minimum temperature represents a much higher increase in volume at ~1.3–2.0 m/km of latitude (Fig. 4), primarily at the range crest is –3 °C to –5 °C (Fig. 3). because the broader snowpack also is thicker. because of higher precipitation northward.

Geosphere, December 2013 1807

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4500 The late season snowpack has evened out the West side—2006 A variations due to individual storms of the early 4000 Feb 2 season. Aside from the overall precipitation, Feb 26 3500 Mar 29 the snowpack is controlled largely by the con- Apr 6 ditions of meltback. The decrease of the snow- 3000 Apr 29 pack elevation northward in the range, its higher June 1 elevation on the east side, and its overall shape 2500 in the spring and early summer all mimic the area covered by glacial lakes. This likeness indi- 2000 cates that the late Pleistocene climate patterns, 1500 though colder, were similar to those of today and that the present-day snowpack can serve as 1000 a template for the much larger and longer-lived snowpacks that accumulated during the gla- 500 cial stages. 4500 East side—2006 B 4000 Vegetation Feb 2 Feb 26 3500 Mar 29 Much of the range is heavily forested, and Apr 6 only in the highest 200 km (between 36.5°N 3000 Apr 29 and 38.2°N lat) is the crest nearly devoid of trees June 1 2500 (Fig. 2). Timberline decreases systematically from ~3700 m in the Mount Whitney region

Elevation (m)2000 Elevation (m) northward to 3500 m at 38.2°N latitude, where timber extends to the range crest. North of this, 1500 the rest of the range is totally forested (Fig. 2). The present-day giant sequoia groves grow on 1000 the west slope from 1500 to 2200 m in eleva-

500 tion, 700–1500 m below timberline (Fig. 7). In 35 36 37 38 39 40 41 general, forests are thicker on the west slope. N latitude (°) The sequoias extend above the lower extent of late Pleistocene glaciers, but between and below Figure 4. Elevation of snowline on the (A) west and (B) east sides current extensively glaciated regions. of snowpack from February to June in 2006, an average snow year. From the National Aeronautics and Space Administration (NASA) PRESENT GLACIATION satellite with MODIS (MODerate-resolution Imaging Spectro- radiometer). The snowline remains higher through the year on the Present-Day Ice east slope primarily due to the orographic effect on storm clouds from the Pacifi c Ocean. U.S. Geological Survey topographic maps made from aerial photos taken in 1976–1978 show 1784 discrete areas of ice that include gla- March 1 April 1 May 1 June 1 ciers and permanent snowfi elds that are identifi ed by blue topographic contours. In this data set, the discrimination of glaciers from snowfi elds and late season snow can refl ect the judg- ment of individual topographers and may not be uniform from area to area. A separate inventory derived from 300 oblique aerial photographs taken in August 1972, during a particularly dry year, identifi ed 497 glaciers and 788 ice patches

North latitude (total 1285), which were tabulated and plotted on USGS 15 min topographic maps (Raub 200 km et al., 2006). These two data sets show a similar, though slightly different, distribution of ice. W e s t l o n g i t u d e The ice masses occur near the crest in the highest part of the range over a distance of 280 km Figure 5. Extent of snowpack during 2006 (an average snow year) for the beginning of from 36.3°N lat to 38.6°N latitude (Fig. 8). The March, April, May, and June. Blue margins indicate areas not entirely snow covered. ice occurs in that part of the range where the From the National Aeronautics and Space Administration (NASA) satellite with MODIS crestal 30 yr average minimum daily tempera- ( MODerate-resolution Imaging Spectroradiometer). ture is –3 °C to –5 °C (Fig. 3). The mapped ice

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200 late summer residual snowpack that provides Width of recent snowpacks 2001 the nourishment that sustains the present-day at 38° N latitude 2002 2003 glaciers and ice masses year after year. When 2004 the snowpack is totally melted earlier in the sea- 150 2005 son, the glaciers recede. 2006 2007 2008 Rock Glaciers 2009 2010 Rock glaciers are tongue-shaped masses of 2011 100 ice covered by bouldery rock debris that are geographically restricted to the higher parts of the southern Sierra Nevada. They occur in and near the same area as the ice masses (Fig. Width of snowpack (km) 50 12). They nestle generally in northerly fac- ing cirques with an average fl ow direction of N10°E. Arcuate ridges in their lower reaches are Width of lake zone parallel to the steep lobate toe. Ongoing move- 0 ment of most rock glaciers is demonstrated by 3456 a steep toe scarp, up to 100 m high, which is March 1 April 1 May 1 June 1 mantled by large fresh angular boulders bal- Month anced at the angle of repose. Disruption of pack trails by movement of rock glaciers is occasion- Figure 6. Width of the snowpack as measured along the 38th paral- ally reported. lel from the beginning of March to the beginning of June during the Some 154 rock glaciers are depicted on geo- years 2000–2011. Note that on 1 May in the average years of 2004, logic maps at 1:62,500 scale (Caudill, 2005). 2005, 2006, 2008, and 2009, the width of the snowpack at the 38th Raub et al. (2006) identifi ed 33 rock glaciers in parallel is ~52 km, i.e., the same width as the lake zone. From the their aerial photograph study. Smaller rock gla- National Aeronautics and Space Administration (NASA) satellite ciers and older inactive rock glaciers have been with MODIS (MODerate-resolution Imaging Spectroradiometer). noted particularly in the northern part of their range (Millar and Westfall, 2008). Field study of several such features indicates that some, and masses include true glaciers, which are defi ned and position of the mapped ice masses (compare probably many, consist of glacial ice under thin as moving masses of ice that are crevassed and Figs. 4, 5, and 8). This convergence of the area (~1–10 m), but continuous, cover of rockfall- are commonly bounded upslope by a master covered by the residual summer snowpack with generated bouldery debris (Clark et al., 1994). crevasse (bergschrund), where they have pulled that covered by the present-day glaciers occurs Although the rock glaciers occur in about the away from the rocky wall of the cirque. They late in the season—by July in a low snow year same span of the range as ice and permanent also include ice patches and permanent snow- and by September in a high snow year. It is this snowfi elds, they are more concentrated toward fi elds in areas largely protected from direct sun- light. The ice occurs preferentially in north- to 5000 northeast-directed cirques, which are largely Timberline shaded, especially in winter. 4500 From south to north, the median elevation of Sequoia groves the ice toes decreases 500 m from 3750 m at 4000 36.5°N to 3250 m at 38.5°N latitude, that is at 2.6 m/km of latitude (Fig. 9). The glaciers are 3500 small—most are less than 500 m long; the longest is the Palisade Glacier at 1.45 km in length. Seven 3000 exceed 800 m (Fig. 10). The elevation difference 2500

between head and toe of most glaciers is less than Elevation (m) 200 m, and only eight exceed 400 m (Fig. 11). Shrinkage of the glaciers has been appreciable in 2000 historic time, as shown by repeat photography. 1500 From 1900 to 2004, the area of 14 of the larg- S N est Sierra Nevada glaciers decreased 31%–78% 1000 (average 55%; Basagic and Fountain, 2011). In 36° 37° 38° 39° 40° 1972, glacial ice and permanent snowﬁ elds cov- North latitude ered ~50 km2 (Raub et al., 2006). Outlines of the satellite-determined present- Figure 7. Elevation of timberline and Sequoia groves as plotted from day summer snowpack show a monthly shrink- U.S. Geological Survey topographic maps. Trees reach to the Sierra age that eventually converges on the elevation Nevada crest south of 36.3°N and north of 38.2°N latitude.

Geosphere, December 2013 1809

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the south (Fig. 12). On average, the elevation of the toes of exposed ice masses is distinctly higher by 200–300 m than the toes of rock glaciers (Fig. 9). This results apparently from the insulating layer of rocky rubble that protects the internal ice of the rock glaciers from the sun’s heat, as well as from melting induced by wind (Clark et al., 1994). The greater concentration of rock glaciers in the south (Fig. 12) may result from lower precipitation, which would tend to Figure 8. Distribution of 1784 increase the ratio of cirque-wall talus to snow. ice masses and 7040 lakes larger The rock glaciers favor coarse-grained granitic 2 than 0.001 km in the Sierra rocks, which produce coarse blocky talus, but Nevada from U.S. Geological some occur in areas of metavolcanic rocks, as in Survey topographic data. The the Ionian Basin. snowpack of 1 May 2006 (an The median elevations of both rock glacier average snow year) is outlined toes and glacier and ice mass toes descend sys- from the National Aeronautics tematically toward the north—the rock glaciers and Space Administration at 3.4 m/km and the ice at 2.6 m/km of latitude (NASA) satellite with MODIS (Fig. 9). In one area near 37.6°N latitude, some (MODerate-resolution Imaging rock glaciers are notably lower in elevation, at Spectroradiometer) data. 2600–2800 m (Fig. 9). These features in the Mount Morrison 15 min quadrangle appear to be older, inactive rock glaciers (Rinehart and Ross, 1964). Rock glaciers are commonly 100–1000 m in length, with a median length of 550 m (Fig. 13). Their maximum size is similar to that of glaciers, but, surprisingly, few small ones, comparable to small glaciers and patches of ice, have been mapped. Probably, most mappers would include small rock glaciers with talus.

4500 PLEISTOCENE GLACIATION Toe of glacier In the Pleistocene ice ages, the ice covered an Toe of rock glacier area of ~20,000 km2, i.e., three orders of mag- 4000 nitude greater than at present. Roughly a third of the range was mantled with ice. It covered broad areas above 1500 m in elevation in the north and above 2500 m in the south. Several of the large western trunk glaciers descended 3500 below 1000 m. The dating of Pleistocene glacial stages in the Sierra Nevada is hindered

Elevation (m) because of the overriding of earlier moraines by later glaciers, the erosion of glacial drift in 2.6 steep canyons, and the limited location and age 3000 of datable adjacent volcanic rocks. The original four units deﬁ ned by Blackwelder (1931)— 3.4 McGee, Sherwin, Tahoe, and Tioga—are still the basis for Sierra Nevada glacial chronology, despite problems uncovered by more recent 2500 36° 37° 38° 39° work (Gillespie et al., 1999). Recent studies N latitude have expanded these four to as many as 15 Figure 9. Elevation of the toes of present-day glaciers (Raub et al., (Gillespie and Zehfuss, 2004), and future work 2006) and of the toes of rock glaciers as determined from geologic will no doubt increase the number. The oldest maps. The slope of least squares lines for each group is shown in relatively well-dated deposit is the Sherwin m/km of latitude. till, dated at ca. 820 ka (Clark et al., 2003). It underlies the Bishop tuff (Kistler, 1966), dated at 767 ka (Crowley et al., 2007).

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1.5 Palisade

From Raup et al., 2004

1.2 Mt Ritter

Norman Clyde E Mid Pallisade Near Lilliput W of Lyell Mt Gilbert 0.9 Mt Powell Kuna

Near Four Gables Middle Palisade Figure 10. Length of glaciers and ice masses in the Sierra Nevada (Raub et al., 2006). Conness Scylla Selected larger glaciers are named. Mt Goethe Lyell 0.6 Mt Humpherys Mt Mendel Dana

Mt McClure Length of glaciers and ice patches (km)

0.3

0 36° 37° 38° 39° N latitude

4200 Vertical extent of ice masses from Raup et al., 2006 4000

3800 o

3600 Figure 11. Elevation of head and toe of 1285 ice masses in the Sierra Nevada (Raub et al., 3400 2006). Glaciers with vertical extent up to 200 m and 400 m are indicated. 3200 Elevation of ice mass toe (m) Elevation increase 3000 from toe to head 200 m 400 m 2800 2800 3000 3200 3400 3600 3800 4000 4200

Elevation of ice mass head (m)

Geosphere, December 2013 1811

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The mapping and separation of moraines on the lower west side of the range are lim- 39°39 ited. Matthes (1930) has mapped the extent Rock glacier of both Wisconsin and the deeply weathered pre-Wisconsin drift (El Portel) in the Yosemite Ice + snow region. Likewise, he has differentiated Wiscon- sin moraines in the San Joaquin River drainage from an older, more extensive pre-Wisconsin drift (Matthes, 1960). The Wisconsin, he suggests, includes both the Tahoe and Tioga stages of Blackwelder (1931), and the pre-Wisconsin 38°38 correlates with Blackwelder’s Sherwin glaciation (Matthes, 1960, p. 48; Huber, 2007). A geochronological study of the Tahoe and Tioga moraines in the Bishop Creek drainage

LAT RG Figure 12. Map showing ice of the southern Sierra Nevada, utilizing the masses (glaciers and ice and accumulation of cosmogenic 36Cl, indicates that snow patches) from U.S. Geo- the moraines mapped as Tahoe stage formed at logical Survey digital elevation N Latitude 170–130 ka, whereas those in the Tioga stage model data, and rock glaciers fall in four groups from 28 to 14.5 ka, and those from geologic maps. 37° in the Recess Peak stage formed from 13.4 to 37 12.0 ka (Phillips et al., 2009). A second study utilizing 10Be in samples from the same and additional moraine on the east side of the Sierra Nevada found Tahoe stage moraines at 144 ± 14 ka and Tioga stage moraines at 19 ± 1.9 ka (Rood et al., 2011). These studies indicate that the Tahoe stage in the southern Sierra Nevada corresponds 100 km with the global marine oxygen isotope stage 36°36 (MIS) 6. A time hiatus of more than 100 k.y. 120°-120 -119119° 118°-118 is indicated between the Tahoe and the Tioga W Longitude glacial stages. In contrast, cosmogenic dating of Tahoe moraines in the type locality at Lake Tahoe by the 10Be and 26Al methods indicates an age of 1.5 69.2 ± 4.8 ka, equivalent to the global marine Ice and snow isotope stage MIS 4 (Howle et al., 2012). Rock glaciers Hence, moraines mapped as Tahoe in the northern Sierra Nevada are apparently only ~50 k.y. older than the Tioga. One interpretation is that 1 in the southern Sierra Nevada, the “younger” Tahoe did not advance as far as the later Tioga, so that its moraines were obliterated by advance of the Tioga ice. In contrast, in the northern Sierra Nevada, the “younger” Tahoe advanced

Length (km) further than the “older” Tahoe and thus obliter- 0.5 ated its moraines, yet these were not covered by the Tioga ice. Limited geochronology has been done on northern west-side glaciers. A 10Be study of S N moraines in Bear Valley found that Tioga stage 0 glaciation in the valley peaked 14,100 ± 1500 yr 36° 39° 37° 38° ago (James et al., 2002). In addition, they noted N Latitude the presence of considerable areas of morainal Figure 13. Comparative length of present-day glaciers and ice deposits older than Tioga stage glaciation. masses (from U.S. Geological Survey topographic data) and rock Recess Peak stage moraines occur high in glaciers (from geologic maps). the cirques just below the small present-day (Matthes ) glaciers. They were initially believed to be nearly as young as the present glaciers, but

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the work of Phillips et al. (2009) indicates that (termed paternoster lakes) occur in high glacial and the partial gap in the crestal lakes at 37.7°N they were deposited between 13.4 and 12.0 ka valleys below the cirques formed at the head of is caused by low regions of the North Fork San (as compared to ca. 14.2–13.0 cal yr B.P. as the glacier. Joaquin River canyon leading to Mono Pass determined by Clark, 1997). The fact that the Some glacial lakes dammed by moraines (3000 m elevation). high-level Recess Peak advance is only a few form near the low-gradient, distal parts of glaci- Proceeding north, forks of the Stanislaus thousand years younger than the last of the pre- ated valleys. The largest and most impressive of and Mokelumne Rivers drain the low region ceding Tioga glaciations demonstrates the very these are found along the east foot of the range near Sonora Pass (38.3°N–38.5°N lat), where rapid retreat from the much more extensive between 37°53′N and 37°27′N lat. Here, large a thinning of the lake zone occurs. In addition Tioga positions. It is this rapid retreat that appar- glaciers in the lower reaches of their canyons to the low elevations formed by the giant can- ently exposed most of the glacial lakes as we have dammed lakes with their terminal and yons of these rivers, the abundant crestal cover see them today, and it helps to account for the recessional moraines. These include Walker of Tertiary volcanic rocks may also inhibit lake paucity of morainal material in this heavily gla- Lake on Walker Creek; Grant Lake, Silver Lake, development. Further north, a prominent gap in ciated sector above the Tioga moraines. Gull Lake, and June Lake on Rush Creek; Con- the lakes at 39.1°N–39.3°N occurs in the head- vict Lake on Convict Creek; Hilton Lakes on waters of the North Fork of American River, Lakes Hilton Creek; and Rock Creek Lake on Rock which includes Donner Pass north of Lake Creek. In addition large lakes—Fallen Leaf and Tahoe. The next well-glaciated region occurs The U.S. Geological Survey 1:24,000 scale Cascade—are dammed by lateral and terminal in the highlands including Bowman Mountain, quadrangle maps depict 7040 lakes in the moraines in the Tahoe Basin. Man Mountain, and Red Mountain between the range, which lie in a nearly continuous N30°W- Other lakes form where lateral moraines of South and Middle Forks of the Yuba River. trending belt that is 450 km long (390 km of N a valley glacier dam smaller tributary streams. The most northerly region of glaciation latitude) in all but the southernmost 100 km of In addition, some high-elevation lakes owe their (extending to 39.8°N lat) lies north of Sierra the range (Fig. 1). Small numbers of lakes are origin to ponding within hummocky neoglacial Buttes. It includes Gold Lake, Salmon Lakes, dammed by landslides, fault scarps, or are of till, and damming by rockfalls and rock glaciers and Sardine Lakes. This lake cluster is drained volcanic origin. The lake listings were edited to from oversteepened cirque walls. on the south by the North Fork of the Yuba exclude these as well as artifi cial lakes dammed Glacial lakes in the entire range occur in the River and on the north by the Middle Fork of as reservoirs and occurring at obviously low elevation range of 1500–4000 m (Figs. 1 and the Feather River. elevation. The largest lake in the Sierra Nevada, 2). The belt of lakes attains its greatest width The effective upper limit of the lakes (the Lake Tahoe (Fig. 1), into which several Pleisto- of 45 km along the south half of the range, and elevation with 1% of the lakes higher) decreases cene glaciers fl owed from the west and south, proceeding north the width decreases at 38.5°N northward from 3900 to 2300 m (4.3 m/km is a structural depression formed by basin-range to 40 km, at 39°N to 35 km, and at 39.5°N to of latitude), the median elevation of the lakes faulting and enlarged by lava-fl ow damming. 15 km. This widening to the south parallels the decreases northward from 3500 to 2000 m (4.5 Some of the major glacial valleys on the greater width of high-elevation terrain (Fig. 1). m/km of latitude), and the lower limit of the west side of the range have been artifi cially The northernmost lakes occur near 39.7°N lati- lakes (the elevation with 1% of the lakes lower) dammed, producing reservoirs in their glaciated tude, somewhat north of Sierra Butte, but the decreases northward from 2600 to 1500 m (3.1 course. These include Salt Spring Reservoir on ill-defi ned northern extent of the Sierra Nevada m/km of latitude; Fig. 16). The high lakes are the North Fork of the Mokelumne River and makes this limit problematic. The southern- controlled by the elevation of the crest of the Hetch Hetchy Reservoir on the Tuolumne River. most glacial lake identifi ed on topographic range and are about coincident with the median Many small ponds constructed for logging maps occurs at 36.096°N lat, 118.574°W long elevation of existing ice. The low lakes track the operations or dug in pastures for cattle watering (Fig. 14). lower elevation of glaciers capable of eroding were deleted. Lakes smaller than 0.001 km2 in In the Sequoia–Kings Canyon National lake basins that have subsequently remained area (~36 m in diameter) were deleted, as were Parks, lakes occur in the upper part of the Tahoe/ unfi lled by sediment and till. other small ponds that proved to be wide spots Tioga glaciated area (Fig. 15). The lake area lies The downward-north slope of the lower lake in streams. in the area of primary snow accumulation. The level (3.1 m/km of latitude) is steeper than, Most lakes are of glacial origin and were glaciated zone where lakes are absent occurs at but similar to, that of the present-day glaciers, carved by ice in bedrock and impounded by lower elevations in the zone of ablation, where which decrease from 3670 m at 36.6°N latitude bedrock sills. For example, of the 302 lakes in ice was largely restricted to the canyon-bound to 3250 m at 38.4°N latitude at 2.3 m/km of lati- the Mount Whitney 15 min quadrangle (Moore, trunk glaciers. tude (Figs. 9 and 16). 1981), only 80, or 26%, are dammed by moraine Prominent embayments with no lakes on the or talus, while the others have bedrock sills. The west side of the lake belt are associated with Moraines and Glacial Canyons bedrock basins are produced by the erosive major river canyons, where low-elevation ter- action of ice and basal water, with the most vig- rain reaches deep into the range (Figs. 1 and 14). Information on glacial moraines is from orous excavation in those areas with preexist- The two south-directed zones of lakes on the 15 min geologic maps, most published in the ing closely spaced joints or fractures (Drewry, south end of the glaciated terrain (Figs. 14 and USGS series and readily accessible on the inter- 1986). In such excavation, the ice at the base 15) fl ank the giant south-directed Kern Canyon. net (Caudill, 2005). Because the moraines are of the glacier fl ows uphill to erode and remove On the west slope, west-protruding highlands preserved differently in different areas, the maps debris and in this way produces closed basins, between canyons support many lakes. The three depict various degrees of detail. Many maps sep- even though the surface and bulk of the gla- main embayments in the lakes between latitudes arate the two major younger Pleistocene moraine cier are fl owing downhill. These quarried lakes 36.7°N and 37°N are from canyons of the three groups that commonly form paired deposits, the often occur in chains down the valley, sited on forks of Kings River. Those from 37.2°N to Tahoe and Tioga of Blackwelder (1931). Others steps. Commonly, multiple such beaded lakes 37.6°N are from forks of the San Joaquin River, simply lump all morainal material in one unit.

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In only a few areas, moraines older than those of the Tahoe stage have been mapped. 40° On the steep east fl ank of the range, the major Pleistocene trunk glaciers occur closer Frazier Cr to the crestal ice fi elds now represented by the glacial lakes (Fig. 14). Because of the asym- M Fk metry of the range, the main trunk glaciers east Yuba of the crest generally extended 5–20 km from Independence Cr Lakes the crest, while those west of the crest extended 25–60 km (Fig. 14). Truckee R Delineation of glacial advances is diffi cult Ward Cr Tioga/Tahoe on the heavily forested west slope of the range, glacial termini where high rainfall has led to weathering and Emerald Bay erosion of deposits and incision of deep can- 39° East Rubicon Cr yons. Vigorous stream action has commonly West removed much of the morainal record associ- W Carson R ated with the major trunk glaciers. In the Merced and San Joaquin River drainages, deposits older S Fk American R than Tahoe/Tioga have been correlated with the Sherwin glaciation on the east slope of the range N Fk Mokelumne (Matthes, 1930, 1960). Bridgeport The areas covered by ice of the Tioga and N Fk Stanislaus Tahoe stages were nearly coincident. Hence, a S Fk Stanislaus common estimate is made in this study of the Lee Vining Cr general position of the combined Tioga-Tahoe 38° termini of glaciers in the major canyons of Cherry Cr June L the west slope. Where morainal evidence is Toulomne R uncertain, this was done by a study of canyon Convict L topography, with the glacier termini located at Merced R the transition in cross section from U-shaped to S Fk Merced R V-shaped and the transition in map plan from straight to crooked (Fig. 14). Pine Cr Lower ice limits generally were higher at Bishop Cr the same latitude on the east side of the range than on the west side. In the southern Sierra San Joaquin R Taboose Cr Nevada, eastern glacier toes were above 1900 m and descended to ~1400 m in the north. In con- 37° trast, several western glaciers descended below 1000 m (Fig. 17). Among the longest glaciers Kings R were those in the canyons of the San Joaquin, Merced, and Tuolumne Rivers, which descended below 1200 m (Figs. 14 and 17). 100 km Kaweah R Moraines in east-side canyons are restricted to higher elevations (Fig. 17) because of the smaller drainage area and lower precipitation east of the crest. Near the central part of the Kern R Tule R range on the east fl ank, high-elevation piedmont slopes at the distal part of the glaciers permitted southernmost lake 36° the ice to exit the confi ning canyons and spread 121° 120° out on low-gradient slopes, causing morainal 119° 118° units of different age to be widely separated and well displayed (Clark et al., 2003; Phillips Figure 14. The distribution of 7040 glacial lakes in the Sierra Nevada primarily generated et al., 2009). In addition, the arid climate and by late Pleistocene Tioga glaciation and the lower limits of glaciation on both sides of the limited vegetation in these areas helped to pre- range. The range crest is shown by a dashed black line, and major drainages are noted. The serve the deposits and render them suitable for zone of snow accumulation is about coincident with the terrain covered by the glacial lakes, detailed study. and the zone of ablation extends from this out to the limits of Tioga-Tahoe glaciation as The lowest elevation reached by the main defi ned by terminal moraines and topographic features. Pleistocene west-side trunk glaciers was markedly lower than the region of extensive snow accumulation and glaciation indicated by the

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119°0'W 118°45'W 118°30'W 118°15'W 37°15'N

37°0'N

36°45'N

36°30'N

Glacial Features of Kings Canyon and Sequoia National Parks Present day ice Glacial lakes

Tahoe Glaciation

Park Boundary 0 2.5 5 10 15 20 Kilometers

Figure 15. Map showing Tahoe glaciation in Sequoia–Kings Canyon National Parks (36.25°N–37.25°N lat; Moore and Mack, 2008) with centers of ice masses and glacial lakes shown.

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5000 Figure 16. Elevation of present-day ice and Lakes and ice divided into 15-minute bands of latitude (27.7 km wide) glacial lakes in 15 min latitude bands from Ice median U.S. Geological Survey topographic maps. 1 % lakes higher Fine lines are least square trend of data 4000 50 % lakes higher arrays, with slope of lines indicated in m/km 99 % lakes higher of north latitude. The minimum elevation of glacial lakes (with only 1% lower) decreases 2.3 from ~2500 m to 1500 m (3.1 m/km of N lat) 3000 from south to north and is dominated by west side lakes. It marks the lower limit of Elevation (m) 4.3 the zone of snow accumulation and active lake basin excavation on the west slope of 2000 4.5 the range.

3.1 S 100 km N 1000 36° 37° 38° 39° 40° N Latitude

3000 Cottenwood Cr alpine glacial lakes. In the central high part of Late Pleistocene moraines the range, the trunk glaciers reached more than 2000 m lower than the general lower limit of East, Tahoe extensive lake-producing glaciation (compare East. Tioga Figs. 14, 15, and 17). Gibbs Cr 2500 West Ta/Ti Equilibrium Line Altitudes George Cr Horton Cr June Lake The equilibrium line altitude (ELA) in a gla- Tule R cier represents the averaged boundary elevation Lee Vining Cr. Lake Tahoe Independence Cr between the upper accumulation zone, where more snow and ice accumulate than melt, and Kern R Big Pine Cr 2000 the lower ablation zone, where more snow and Green Cr ice melt than accumulate. Above the ELA, the S N Fk Oak Cr S S Fk American R ice and snow accumulates season after season, Kaweah R M continually increases in thickness, consolidates, E S Fk Truckee R and begins to fl ow downhill. Below the ELA, Bishop Cr Stanislaus R the fl owing ice melts faster than it is delivered. Pine Cr Elevation (m) 1500 As it fl ows downhill into warmer sites, melting increases until all ice disappears at the glacier S W Carson R Goose Lake toe. The position of the ELA moves uphill as the Kings R M N Fk Yuba R average temperature increases or the snowfall Merced R decreases; it moves downhill with temperature N Rubicon Cr N Valley Cr decrease or snowfall increase. S Fk Merced R N Fk Mokelumne R The zone of accumulation is largely con- 1000 trolled by factors that deliver snow to the range Big Cr O N Fk American R Tuolumne R and enable part of it to remain until the next sea- San Joaquin R O son. Average annual snowfall and temperature are important, and they are controlled in part by V= 210 H 100 km N elevation. The zone of melting is also controlled S Merced R: El Portel Oo by temperature and precipitation, but topogra- 500 O 36° 37° 38° 39° 40° phy plays an increasing role once the ice begins fl owing. In the accumulation zone, snow and ice N Latitude are delivered by fall from the atmosphere, but in the ablation zone, they are delivered primar- Figure 17. Elevation of the lower limit of major glaciers on both sides of the range (with 210× ily by fl ow on the ground surface. When the ice vertical exaggeration). East side moraines are divided into the Tioga (Ti) and Tahoe (Ta) stages, from the accumulation zone fl ows downhill, it and those on the west side are undivided. Ice limits in the major river canyons are labeled. The will seek out lower terrain in the major river outlined red dots are termini of west side Sherwin-age glaciers (Matthes, 1930, 1960). canyons. Here, the ice streams will merge and

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4000 mated the system was at an elevation of 3170 m Equalibrium line elevation Toe to headwall altitude ratio (THAR)= 50% in the drainage of the South Fork of the Kings 3500 River (36.9°N lat). This places the paleo-ELAs East slope somewhat below the median elevation of the West slope lakes (Fig. 17). 3000 99% lakes higher An estimation of the ELAs for the main drainages of both the west and east slopes of the 2500 range was made by using the toe-to-headwall- 3.5 m/km average-ratio (THAR) method. For each major 2.7 m/km

Elevation (m) drainage, the termini elevation of late Pleisto- 2000 cene glaciers (primarily Tioga stage; Fig. 17) was compared with the headwall elevation of 1500 3.1 m/km the same glacial system. The average of these two elevations, when assuming a THAR ratio of 1000 0.5, became the ELA estimate. The results (Fig. 36° 37° 38° 39° 40° 18) indicate an average west slope ELA (based N latitude on 22 glacier measurements) that is nearly par- Figure 18. Comparison of the equilibrium line altitude (ELA) cal- allel to, and 400–600 m below, the average east culated using the toe-to-headwall-altitude ratio (THAR) with an slope ELA (based on 32 glacier measurements). assumed ratio of 0.5 for glaciers on both the east and west slopes Moreover, the elevation trend with latitude of of the range. The least squares trend of the lower limit of lakes is the west side ELAs is parallel with, and only shown from Figure 16. 200–300 m above, that of the elevation of the lowest west side lakes (Fig. 18). This correspondence of the rangewide west thereby increase in longevity. On a regional smallest and would have been comparable in slope ELA calculated from the distribution of scale, this results in a more continuous area of size to the average present one at the beginning the late Pleistocene ice with the lower limit of ice above the ELA than below it, as shown by of May. This would then allow the previous sea- the lake zone suggests that the lake zone can be the late Pleistocene ice cover in Sequoia–Kings son’s unmelted snow to be covered by snow of a rough gauge of the position of the accumula- Canyon National Park (Gig. 15). The upper part the next season. The resulting buildup of snow tion zone. Therefore, the generalized position of the glaciated area is more continuous, with and ice would form the accumulation zone and of the late Pleistocene ELAs occurs close to, only high ridges and peaks exposed above the then fl ow downslope. That movement carved but somewhat above, the lower limit of the gla- ice. The lower reaches are divided into discrete the lake basins in the zone of accumulation cial lakes. trunk glaciers that have sought out, and fl ow and fed trunk glaciers that moved downslope to down, the large preexisting river-cut canyons. concentrate ice largely in previous river valleys. CONCLUSIONS Abundant lakes mark the upper part of the glaci- This movement downslope into warmer zones ated area, whereas lakes are not common in the created the ablation zone, where eventually the The 600-km-long Sierra Nevada underwent lower part. glacier terminated as all ice melted. extensive Pleistocene glaciation in its northern The upper part of the Sierra Nevada glacial The ELA is commonly approximated by two 500 km. In this work, new and existing data are system was erosive over a broad highland area methods using empirical ratios derived from evaluated to examine the rangewide weather as the evenly distributed ice in the accumulation modern bare ice glaciers (Meierding, 1982). and the distribution of the present-day snow- zone moved to lower elevation. The scattered The fi rst is to measure the snow accumulation pack, glacial lakes, existing glaciers and rock small lake basins record this erosive action. The area relative to the total area of the glacier. The glaciers, and Pleistocene glaciers as determined lower part of the glacier system, where melting altitude of the ELA is taken where the ratio of by mapped moraines and topographic evidence. was taking place (the ablation zone), was largely the accumulation area to the total glacier area Presently ~1700 small glaciers and ice masses confi ned to major preexisting river canyons. (AAR) is empirically established, e.g., 0.65. The at 3000–4000 m elevation occur along 240 km Few lakes were formed or survived in this zone, second method assumes a ratio of elevation of of the range crest and cover ~50 km2. These probably because postglacial sedimentation the equilibrium line relative to the total range in glaciers are generally less than 500 m long, and dominated in the lower-graded slopes. elevation of the glacier from head to toe (toe-to- the median elevation of the lower limit of the A comparison of the area of present-day headwall altitude ratio or THAR), e.g., 0.4–0.5. glaciers descends north at 2.4 m/km. Repeat snow accumulation with the area occupied by Series of models of the movement of ice dur- photography shows a historical shrinkage, with glacial lakes shows a marked similarity. The ing the last glacial advance in the Kings river 14 of the largest glaciers having lost on average area of the snowpack of 1 May 2006 (an aver- drainage (Kessler et al., 2006) were performed about half their area from 1900 to 2004. age snow year) closely encloses the distribution by making assumptions on the orographically About 154 rock glaciers show a similar dis- and shape of the area of glacial lakes (Fig. 8). infl uenced glacier mass balance based on mea- tribution as the present-day glaciers but aver- During glacial times, the snowpack would have sured functions on modern glaciers in west- age 150–200 m lower. They apparently owe been much larger at the same date and would ern North America (Meier et al., 1971; Mayo, their lower elevation to the insulation and wind have remained large through the seasons. We 1984). Models were tested to fi nd the ELA that protection provided by a mantle of bouldery speculate that in the late Pleistocene glacial produced the best approximation of the limit of debris on ice. stages, the snowpack at the end of the summer glacial ice in the main Kings Canyon glacial The base of the present-day snowpack, the melting season in September-October would be system. The ELA that most closely approxi- snowline, generally decreases in elevation

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northward, and it is 500–1000 m higher east of Sierra Nevada, California: U.S. Geological Survey west asymmetry in Sierra Nevada glacier length during Miscellaneous Investigations Series Map I-1885. the Last Glacial Maximum: Journal of Geophysical the crest than west of the crest. Basagic, H., and Fountain, A.G., 2011, Quantifying 20th Research, v. 111, F02002, doi:10.1029/2005JF000365. About 7040 alpine lakes occur over all but the century glacial change in the Sierra Nevada, Cali- King, C., 1871a, Mountaineering in the Sierra Nevada southern unglaciated crestal region of the range. fornia: Arctic, Antarctic, and Alpine Research, v. 43, (edited by F.P. Farquhar, 1935): Boston, Massachu- no. 3, p. 317–330, doi:10.1657/1938-4246-43.3.317. setts, J.R. Osgood & Co., 292 p. These glacial lake basins, at 1500–4000 m ele- Blackwelder, E., 1931, Pleistocene glaciation in the Sierra King, C., 1871b, On the discovery of actual glaciers in the vation, were largely exposed and fi lled as ice Nevada and Basin Ranges: Geological Society of Mountains of the Pacifi c Slope: American Journal of rapidly retreated at the end of the Tioga stage America Bulletin, v. 31, p. 865–922. Science, v. 1, p. 157–167. Caudill, N., 2005, Sierra Nevada Batholith Map Mosaic Kistler, R.W., 1966, Geologic Map of the Mono Craters at 15–20 ka. The average elevation of the lower Project: University of North Carolina, http://geomaps Quadrangle, California: U.S. Geological Survey Geo- limit of the lakes descends north at 3.1 m/km. In .geosci.unc.edu (accessed 21 August 2013). logic Quadrangle Map GQ-452, scale 1:62,500. Clark, D.H., 1997, A new alpine lacustrine sedimentary Matthes, F.E., 1930, Geologic History of the Yosemite Val- May of an average year, the current snowpack record from the Sierra Nevada: Implications for late- ley: U.S. Geological Survey Professional Paper 160, mimics in area the zone of glacial lakes and, Pleistocene paleoclimate reconstructions and cosmo- 137 p. like the glacial lakes, also decreases in elevation genic isotope production rates: Eos (Transactions, Matthes, F.E., 1960, Reconnaissance of the Geomorphology American Geophysical Union), v. 78, p. F249. and Glacial Geology of the San Joaquin Basin, Sierra about the same amount both northward and west Clark, D.H., Clark, M.M., and Gillespie, A.R., 1994, Debris- Nevada, California: U.S. Geological Survey Profes- of the crest. This correspondence suggests that covered glaciers in the Sierra Nevada, California, and sional Paper 329, 62 p. climate patterns—though colder—were similar their implications for snowline reconstructions: Qua- Mayo, L.R., 1984, Glacier mass balance and runoff research ternary Research, v. 41, p. 139–153. in the U.S.A.: Geographic Annual, ser. A, Physical in the late Pleistocene to those of the present Clark, D., Gillespie, A.R., Clark, M., and Burke, B., 2003, Geography, v. 66, no. 3, p. 215–227. day. It also indicates that the area of lakes is a Mountain glaciations of the Sierra Nevada, in East- Meier, M.F., Tangborn, W.V., Mayo, L.R., and Post, A., 1971, erbrook, D.J., ed., Quaternary Geology of the United Combined ice and water balances of Gulkana and Wol- gauge of the zone of snow accumulation. States: Reno, Nevada, Desert Research Institute, verine glaciers, Alaska, and South Cascade glacier, The buildup of the Pleistocene ice cap caused INQUA 2003 Field Guide Volume, p. 297–311. Washington, 1965 and 1966 hydrologic years: U.S. Geo- it to fl ow to lower elevation down existing Crowley, J.L., Schoene, B., and Bowring, S., 2007, U-Pb dat- logical Survey Professional Paper 715-A, 23 p. ing of zircon in the Bishop Tuff at the millennial scale: Meierding, T.C., 1982, Late Pleistocene glacial equilibrium stream-cut canyons considerably below the Geology, v. 35, no. 12, p. 1123–1126, doi:10.1130 line altitudes in the Colorado Front Range: A compari- zone of glacial lakes. The elevation of the ter- /G24017A.1. son of methods: Quaternary Research, v. 18, p. 289– mini of these glaciers is lowest (below 1000 m) Dalrymple, G.B., 1964, Potassium argon dates of three 310, doi:10.1016/0033-5894(82)90076-X. Pleistocene interglacial basalt fl ows from the Sierra Millar, C.I., and Westfall, R.D., 2008, Rock glaciers and in the central high and wide part of the range Nevada, California: Geological Society of America related periglacial landforms in the Sierra Nevada, in the drainages of the San Joaquin, Merced, Bulletin, v. 75, p. 753–758, doi:10.1130/0016-7606 CA, USA; inventory, distribution and climatic rela- (1964)75[753:PDOTPI]2.0.CO;2. tionships: Quaternary International, v. 188, no. 1, and Tuolumne Rivers. Despite the fact that the Daly, C., Neilson, R.P., and Phillips, D.L., 1994, A statistical- p. 90–104, doi:10.1016/j.quaint.2007.06.004. northern crest of the range is lower in eleva- topographic model for mapping climatological pre- Moore, J.G., 1981, Geologic Map of the Mount Whitney tion, the northern increase in precipitation and cipitation over mountainous terrain: Journal of Applied Quadrangle, Inyo and Tulare Counties, California: Meteorology, v. 33, p. 140–158, doi:10.1175/1520 U.S. Geological Survey Geologic Quadrangle Map decrease in temperature enabled the main trunk -0450(1994)033<0140:ASTMFM>2.0.CO;2. GQ-1545, scale 1:62,500. glaciers to descend nearly as low as those from Dozier, J., Painter, T.H., Rittger, K., and Frew, J.E., 2008, Moore, J.G., and Mack, G., 2008, Limits of Tahoe Gla- the higher part of the range to the south. 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