Quartz Hills

The Quartz Hills occupies an area about 20 km (12 mi) long and between 1 and 18 km (0.62 and 11.18 mi) wide that lies on the left side of the Reedy Glacier. Its landscape exhibits mature, steep, alpine relief, including horns, arêtes, cirques, and glacially carved valleys. They range from 1,180 m (3,870 ft), the surface elevation of Reedy Glacier, to about 2,200 m (7,200 ft) in elevation. In part, the Quartz Hills contains an extensive, low-angled slope, known as the Quartz Hills bench. It rises southward over a distance of about 4.5 km (2.8 mi) from about 1,300 m (4,300 ft) to more than 1,700 m (5,600 ft) in elevation. Within the Quartz Hills, ice cover is limited to perennial patches with the exception of one small, isolated glacier.[3][4]

Well-preserved drift sheets and moraines form a veneer across the ice-free areas of the Quartz Hills. In 1968, Mercer identified three distinct drifts, the Reedy I, Reedy II, and Reedy III drifts, in order of decreasing age, based on position, composition, and relative weathering.[3] Later, more detailed, mapping based upon drift position, composition, relative weathering, and cosmogenic surface exposure dating of glacial erratics recognized additional distinct glacial deposits designated as the Reedy A, B, C, D, and E drifts. The older of these drifts represent multiple periods of time during the mid to late Cenozoic when Reedy Glacier was significantly thicker than today. Thin patches of even older, highly weathered, undifferentiated drift lacking definite limits occur in the Quartz Hills. The Reedy III drift, was deposited when the ice surface near the head of the glacier was about 40 m (130 ft) higher than today and at the mouth of Reedy Glacier was about 500 m (1,600 ft) thicker during the Last Glacial Maximum. The deposition of Reedy B drift accumulated when Reedy Glacier was thicker and covered a larger aerial extent of the Quartz Hills during Marine Isotope Stage 6. The Reedy D drift represents the deposits of Reedy Glacier that accumulated when it covered even larger parts of the Quartz Hills more than 2.5 Myr ago. The oldest dated drift, Reedy E drift, represents the deposits of Reedy Glacier when it covered the Quartz Hills at least 5 Myr or more ago.[4]

Finally, within the Reedy Glacier valley walls, outcrops of about 100 to 150 m (330 to 490 ft) of lithified diamictites and rhythmites (interbedded stratified mudstones and sandstones) occur unconformably overlying pre-Cenozoic bedrock. These diamictites and rhythmites, which are assigned to the Quartz Hills Formation of the Sirus Group, nonconformably overlie a glacially grooved and striated undulating surface eroded into granites and schistose rocks. The analysis of samples from the Quartz Hills Formation found it to be essentially barren of organic matter. The extremely rare palynomorphs recovered from it include: two specimens of an angiosperm pollen of unknown affinity and a specimen each of Podocarpidites and Chenopodiaceae pollen. The conifer specimen is similar to that recovered from other Sirius Group sediments. One sample from the Quartz Hills Formation yielded marine diatoms. These fossil diatoms included Pliocene-Pleistocene species Actinoqdus artinochilus, Tltalassiosira lenlittinosa, Tltalassiosira oestrupii and Tltalassiosira lorokina. Other samples only yielded freshwater diatoms, including well-preserved Stephanodiscus sp. , which is a Neogene freshwater diatom.[5]

Within the Quartz Hills, the exposed bedrock consists predominantly of coarse-grained granite gneiss; smaller amounts of orthoclase-feldspar and plagioclase-feldspar granites; and dark, fine-grained metasedimentary rocks. The granite gneiss and granites are plutonic rocks of the Wisconsin Range Batholith. Within the Quartz Hills, the dark, fine-grained metasedimentary rocks consist of gray to black phyllites, metagraywackes, and impure quartzites of the LaGorce Formation. They and associated mafic metavolcanic rocks of the Wyatt Formation are both intruded by granitic rocks of the Wisconsin Range Batholith. Therefore, these granitic rocks are not the continental crust upon which the sedimentary and volcanic rocks of LaGorce and Wyatt formations were deposited prior to the Ross orogeny.[4][6]

• Dolan Peak