Twin Spruce Monzogranite
Granite. Proterozoic, about 2,500 to 1,000 million years old. 2 crags on this site have their map point on it.
What the map says
Gray, fine- to medium-grained, equigranular, massive to weakly foliated biotite-muscovite monzogranite and rare granodiorite. Twin Spruce Monzogranite intrudes rocks of Boulder Creek Granodiorite (XgdB) in a complex pattern. Weathers tan in rounded outcrops. Preliminary U-Pb zircon data suggest age about 1,704±6 Ma (W.R. Premo and K.S. Kellogg, unpub. data, 2007), supporting the observation (Gable, 1980) that the unit is younger than Boulder Creek Granodiorite. Two samples of rock petrographically similar to Twin Spruce Monzogranite from within the Boulder Creek batholith have U-Pb zircon dates of 1,443±19 Ma and 1,412±25 Ma (W.R. Premo, unpub. data, 2005), indicating a local resurgence within the batholith of magmatism of the Berthoud Plutonic Suite. Twin Spruce Monzogranite also referred to as Twin Spruce Quartz Monzonite (for example, Gable, 1980); the lithic term monzogranite follows Streckeisen (1976)
1:100,000 sheet: Kellogg and others, 2008, USGS Geologic Investigations Series 3000 (2 crags). 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.