Geology of the Basin Quadrangle, Montana
<p>The Basin quadrangle, in the northern part of the Boulder Mountains between Butte and Helena, Montana, is underlain principally by igneous rocks that…
Public-domain full text preserved in the Mountain Man Mining Library. Original source: pubs.usgs.gov.
Geology of the Basin Quadrangle, Montana Author: Ruppel, Edward Thompson Year: 1957 Category: Report <p>The Basin quadrangle, in the northern part of the Boulder Mountains between Butte and Helena, Montana, is underlain principally by igneous rocks that include Late Cretaceous quartz latitic and andesitic Elkhorn Mountains volcanics, quartz monzonite and related rocks of the Boulder batholith, Oligocene(?) quartz latitic volcanic rocks, and late Miocene(?)-early Pliocene(?) rhyolitic volcanic rocks. Sedimentary rocks of the Late Jurassic Morrison formation, the Early Cretaceous Kootenai formation, and the Early Cretaceous lower part of the Colorado formation, crop out in the northwest part of Tags: usgs, auriferous gravels Source: ://pubs.usgs.gov/of/1958/0087/plate-1.pdf