The Wall

Rock, from the geologic map

Langhoff Gulch Granite. Mesoproterozoic, about 1,600 to 1,000 million years old.

Gray, medium-grained, equigranular to inequigranular, massive to weakly flow-foliated, syenogranite, monzogranite, and granodiorite; mostly monzogranite. Contains about 25–35 percent quartz, 20–40 percent plagioclase, 12–45 percent microcline, 4–20 percent biotite, 1–2 percent muscovite, trace to 1 percent sphene, and trace amounts of zircon and apatite; locally contains sparse rutile and garnet. Almost all modal analyses from 19 stained slabs indicate monzogranite composition. Unit typically weathers to distinctive reddish-brown to light grayish-brown rounded to blocky outcrops. Langhoff Gulch, for which unit is formally named, is located in NE1⁄4 sec. 31, T. 12 S., R. 79 W., about 7 km southeast of the town of Granite. Dikes and bodies of rock included with Langhoff Gulch Granite intrude Elephant Rock Granite (Yge) in many places, such as small stocks of massive to foliated, generally gray to pinkish-gray, medium-grained monzogranite and subordinate quartz monzonite in Buena Vista East quadrangle (Keller and others, 2004). New U-Pb zircon age from location U is 1,441±54 Ma (Moscati and others, 2017). The name Langhoff Gulch Granite is herein formalized and location U on map (38°59 17"N., 106°12 45"W., on the USGS Harvard Lakes quadrangle), in a small abandoned quarry near the mouth of Langhoff Gulch, is hereby designated the type locality. The Langhoff Gulch Granite at two other locations has U-Pb zircon ages of 1,435±26 Ma and 1,438±11 Ma (Moscati and others, 2017). Unit includes granitic rocks in Climax quadrangle (McCalpin, Temple, and others, 2012) that are “similar in texture and composition” to the 1,442±2 Ma Silver Plume Granite (Graubard and Mattison, 1990), which is exposed about 50 km northeast of the map area

This is the map unit under this crag's map point, read from the 1:100,000 sheet (Kellogg and others, 2017, U.S. Geological Survey Scientific Investigations Map 3382). The point can be a few hundred metres from the rock, a cliff often stands on the line between two units, and at that scale a line on the map is about 100 m wide on the ground, so the wall itself may be the neighbouring unit. Every crag on this unit: Langhoff Gulch Granite. Geology data: Macrostrat (CC BY 4.0), serving USGS and Colorado Geological Survey maps.