Both are finely engraved and very detailed charts by the U.S. Geological and Geographical Survey of the Territories from Hayden's 12th Annual Report published in 1883. The two maps are color coded to indicate geological formations, but are also excellent geographical depictions of the region. They are particularly useful for tracing the movements of early fur traders and immigration patterns as their routes are shown. The former shows all land from the Green River Basin in the east to the Bear River Range to the west. It extends north to include part of Gary's Lake and details the Aspen, Salt River and Wyoming Ranges in the north, and extends south below Bear Lake to Logan. Further locates numerous settlements and includes Fremont’s Lake adjacent to today's Pinedale. It was surveyed by H. Gannett. The latter is the northern sheet of the pair. It extends north from Gray's Lake all the way to the Tetons, Jenny and Jackson's lakes. To the east is Fremont's Peak and at the west is the Henry's Fork of the Snake River, Willow Creek, and Blackfoot Peak. This chart was surveyed by O. St. John assisted by G.R. Bechler and F.R. Clark. Both feature beautiful color and remarkable detail, with contour intervals at 200 feet and scale of 1 inch = 4 miles. Fine pair of early geological maps that are seldom seen together.

References: Wheat (TMW) 1296.

Condition: A

Issued folding, now pressed and backed with archival tissue. Light toning along a few folds and the top and bottom margins a little chipped in former.