Till of Pinedale age

What the map says

Subangular to subrounded boulders, cobbles, and pebbles set in a sandy silt to silty sand matrix. Prominent, sharp-crested moraines are numerous; rugged knob-and-kettle topography is well developed in some areas. Gullying is negligible. Moraine-dammed lakes, swamps, and perennial kettle-hole ponds are abundant. Most soils (A and B horizons only) are 45-75 cm thick. Less than 5 percent of stones in B horizon are rotted. Description from Gable and Madole (1976). Patterned lines within unit indicate trend of lateral and terminal moraines. Pinedale glaciation probably began in the region more than 35,000 years ago, and occurred in several pulses. Last major advance of Pinedale glaciers approached its maximum about 22,000 years ago, and these glaciers began to recede from their terminal moraines between 13,000 and 15,000 years ago. Most Pinedale glaciers were probably gone by 10,000-11,000 years ago (age data from Madole and Shroba, 1979, pages 128-129). GRI Source Map ID 141 (I-1973). Lithology: unconsolidated.

1:100,000 sheet: National Park Service Geologic Resources Evaluation program, 2006, National Park Service (11 crags). A contact line at that scale is about 100 m wide on the ground.

Mostly nonsorted and nonstratified, subangular to subrounded boulders to granules in a silty sand matrix. Material less than 2 mm in diameter is estimated to be 20–40 percent of unit. This material consists chiefly of poorly sorted sand and ≤20 percent silt and ≤5 percent clay. Unit commonly forms large prominent, sharp-crested lateral and end moraines that are very bouldery and have distinct constructional morphology. Deposits in some areas have well-expressed knob-and-kettle topography. Surface soils have A/Cox profiles on moraines with narrow crests and A/Bw/Cox and A/Btj/Cox profiles on moraines with broad crests. Surface and near-surface O and E soil horizons are locally present. Cambic (Bw) and weak argillic (Btj) horizons are thin (10–40 cm) and commonly contain 1–5 percent more clay than the underlying till (<2 mm size fraction). Most of the biotite-rich granitic and gneissic clasts within the soil are unweathered, and disintegrated clasts are rare. Unit locally includes deposits of stratified drift, mass-movement and glacial deposits, undivided (Qmg), tills of the Satanta Peak and Triple Lakes advances of Benedict (1985), about 12–10 ka (Davis, 1988), till of Bull Lake age (Qtb), colluvium (Qc) and other mass-movement deposits, and valley-floor alluvium (Qva); locally may include till of pre-Bull Lake age. Radiocarbon (14C) and cosmogenic-exposure ages indicate that till of unit Qtp is about 30–12 ka (Nelson and others, 1979; Madole, 1986; Schildgen and Dethier, 2000; Benson and others, 2004, 2005). Subsurface deposits and locally some surface deposits of unit Qtp may be older than 30 ka, because uranium-series ages of travertine in the northern Yellowstone area suggest an early advance of Pinedale ice about 47–34 ka (Sturchio and others, 1994). Estimated thickness 1.5–30 m

1:100,000 sheet: Kellogg and others, 2008, USGS Geologic Investigations Series 3000 (10 crags). A contact line at that scale is about 100 m wide on the ground.

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