Boulder Creek Granodiorite

What the map says

Light- to medium-gray, medium- to coarse-grained, weakly to strongly foliated granodiorite composed of oligoclase, quartz, microcline, and 5-15 percent biotite; phenocrysts of microcline (1-4 cm long) common. Forms a large elongate pluton in south-central part of map area, and small bodies 4 km northeast of Lake Estes, 1 km east of Lead Mountain (Never Summer Mountains), and in southeast corner of map area. Rb-Sr age for Boulder Creek Granodiorite in plutons southeast and northeast of map area is 1,664+/-40 Ma (Peterman and others, 1968, p. 2287). GRI Source Map ID 141 (I-1973). ** Areas where numerous dikes of Silver Plume Granite (Ysp) intrude Boulder Creek Granodiorite [indicated by stippled regions on source paper map]. Lithology: intrusive igneous (plutonic).

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

Gray, coarse-grained, equigranular to porphyritic, massive to weakly foliated biotite±hornblende±muscovite monzogranite, granodiorite, and tonalite. Forms large intrusive body (Boulder Creek batholith) west of Boulder (Gable, 1980). Typically weathers into grayish-tan rounded outcrops. Mean U-Pb zircon date from numerous analyses is 1,716±3 Ma (W.R. Premo and K.S. Kellogg, unpub. data, 2007), which supports earlier U-Pb zircon dates of 1,725 Ma (Stern and others, 1971) and 1,721±15 Ma (Premo and Fanning, 2000)

1:100,000 sheet: Kellogg and others, 2008, USGS Geologic Investigations Series 3000 (52 crags). A contact line at that scale is about 100 m wide on the ground.

Mottled black and white medium- to coarse-grained, foliated granodiorite, locally porphyritic and may include some quartz monzonite. Age about 1.72 billion years (Hedge and others, 1967, p. 555).

1:100,000 sheet: Trimble and others, 2003, U.S. Geological Survey Geologic Investigations Series I-856-H (14 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.