Quartzite

What the map says

White, gray, and purplish-gray, medium- to coarse-grained quartzite and quartz-rich gneiss and schist. Locally conglomeratic with clasts of coarser grained, lighter colored quartzite that are commonly tectonically stretched. Generally contains as much as a few percent muscovite and traces of garnet, magnetite-ilmenite, and epidote. Unit includes muscovite-quartz gneiss and schist layers and some calc-silicate gneiss lenses. Forms a large, synformal body (Coal Creek quartzite) in southern part of Eldorado Springs 7.5-minute quadrangle (Wells, 1967) and northern part of Ralston Buttes quadrangle (Sheridan and others, 1967); most contacts with Twin Spruce Monzogranite (YXgT) are sheared, and relative age of quartzite and intrusive rocks is uncertain. Gable (1980) and Wells and others (1964) described intrusive contacts between rocks of the Boulder Creek batholith and quartzite. However, preliminary detrital zircon evidence suggests quartzite is younger than the batholith (J.N. Aleinikoff, unpub. data, 2007), a suggestion supported by structural and stratigraphic evidence (McCoy and others, 2005). If this interpretation is correct, the depositional age of quartzite is less than 1,704±6 Ma

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

Served by Macrostrat (CC BY 4.0). The wording is the map's own, quoted as a fact about the mapped unit, not about any one wall.