Origin and Development of the Three Forks Basin, Montana

Magnitude, extent, and potential sources of nitrate in ground water in the Gallatin Local Water Quality District, southwestern Montana, 1997-98

“…Structurally, the Gallatin Valley intermontane basin composes the eastern two-thirds of an eastwardtilted graben (Robinson, 1961). The southwestern basin boundary is not flanked by obvious faults and might be a depositional contact between Cenozoic basin fill and pre-Cenozoic bedrock.…”

“…The southwestern basin boundary is not flanked by obvious faults and might be a depositional contact between Cenozoic basin fill and pre-Cenozoic bedrock. The eastern boundary of the Gallatin Valley is a series of steep normal faults along the fronts of the Bridger and Gallatin Ranges (Robinson, 1961). Gravity data indicate that more than 6,000 ft of Cenozoic sediments fill the basin at its deepest point, east of Bozeman Hot Springs (Noble and others, 1982).…”

“…However, the formation crops out extensively to the west of the GLWQD. These fine-grained, dominantly lacustrine, tuffaceous sediments underlie the Sixmile Creek Formation in most, if not all, of the Gallatin Valley (Hackett and others, 1960;Robinson, 1961 (Slagle, 1995a). Transmissivity values determined from four aquifer tests range from 40 to 2,300 ft2/d (Hackett and others, 1960).…”

The Cenozoic rocks; a discussion to accompany the geologic map of the United States

“…They were originally termed the "Bozeman lake beds," but most of them are fluviatile rather than lacustrine in origin, and modern work indicates that they are heterogeneous, including deposits of many Tertiary ages, now collectively referred to as the Bozeman Group (Robinson, 1961(Robinson, , p. 1003(Robinson, -1004 (Kelley and Silver, 1952, p. 120-123). The first is a red bouldery deposit with many volcanic clasts, the second a light buff tuffaceous clay.…”

Tectonics of the Intermountain Seismic Belt, Western United States: Microearthquake Seismicity and Composite Fault Plane Solutions

“…The geology is complex and various hypotheses have been presented for its origin. Robinson (1961) summarized these ideas and presented a more coherent though still incomplete picture of the region, which is used in a comparison with our data. The most recently active faults in the area (late Miocene and Pliocene) are the high-angle faults along the Bridger Range (Fig.…”