1. Geologic map of the Nelson quadrangle, Lewis and Clark County, Montana Yale Public content 2003. 2003-12-19T20:27:20Z. 2011-03-03T23:26:44Z. Geological Survey (U.S.). U.S. Dept. of the Interior, U.S. Geological Survey ; For sale by USGS Information Services. English. Public. Montana and Lewis and Clark County.