Porphyroblastic quartz-biotite-muscovite schist of White Ranch
Gneiss, schist & quartzite. Paleoproterozoic, about 2,500 to 1,600 million years old. 1 crag on this site has its map point on it.
What the map says
Silvery gray schist layers composed mostly of fine- to medium-grained, foliated, locally porphyroblastic schist composed principally of quartz, biotite, and muscovite, with small amounts of sillimanite and staurolite (Wells, 1967). Porphyroblasts include andalusite, cordierite, and garnet; some andalusite crystals in central Ralston Buttes 7.5-minute quadrangle are as long as 30 cm (Sheridan and others, 1967). Where rock is relatively unstrained, original sedimentary structures (graded bedding and cross bedding) are visible. Locally contains lenses of meta-conglomerate and calc-silicate rock (Sheridan and others, 1967). U-Pb zircon ages from clasts in metaconglomerate are ≈1,750 Ma, which is maximum depositional age of sediments in basin that includes rocks of this unit
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.