Montana High Potassimn Igneous Province – Crazy Mountains to Jordan, Montana, July 20–27, 1989 Volume T346

Published by the American Geophysical Union as part of the Field Trip Guidebooks Series, Volume 346.

On this field trip, we will visit some of the major and minor alkalic igneous centers within an area of about 120,000 km2 in central Montana (Figure 1.1). This broad area has been of particular interest to petrologists for more than 90 years because of the abundance of alkalic rocks, including some rare varieties that were described in several excellent reconnaissance studies in the late 19th century, and three decades of modern petrologic, isotopic, and geophysical studies. Access is relatively easy and the rocks are well exposed.

The time of earliest arrival of man in the Montana-Wyoming area is controversial. However, early man was well established by 11,500 yr B.P. as shown by several sites of Clovis-style stone artifact points in Montana and Alberta. Well-dated sites in Montana range from about 11,500 yr B.P. to recent historic time. The northern plains were occupied by the plains woodland people from the east in about 100 A.D.