GEOLOGICAL MAPPING OF THE EOCENE BRIDGER FORMATION, SW WYOMING

Geological mapping of the Eocene Bridger Formation, Units B through E has documented a number of marker beds. Limestones or tuffs and other widespread marker beds were followed and mapped in the field on topographic maps or on aerial photographs, and then transferred into ArcGIS format. The marker beds were found to be generally continuous across the basin, facilitating the development of a reliable stratigraphy of the Bridger Formation.

Mapping of the Upper Bridger Formation (Units C – E), on ten 1/24,000 topographic quadrangles from the southern part of the Bridger exposures was published by the Wyoming State Geological Survey (Murphey and Evanoff 2007). These maps included mapping of Bridger B by Leonard Brand.

Finished maps of the rest of Bridger B are now available, all on 1/24,000 topographic quadrangles. There is also a revised map of the Devils Playground quadrangle, which includes additional mapped marker beds not on the original published Devils Playground map.

The mapping of Bridger B was done in the same way as for the published maps of the southern quadrangles. Twelve marker beds were mapped over all or most of the basin, and two others were more localized. The limestones reflect intervals when the basin was occupied by shallow lakes, which were periodically overwhelmed by volcanic input from northern Wyoming.

The Bridger B maps are available at this time in two formats. Pdf maps can be printed at 11 x 17 inches, and at full topographic quadrangle size of 28 x 34 inches. The second set of files is in ArcGIS format, and can be used as a georeferenced base for additional mapping if desired. These files can be accessed on the following two websites:

http://ftp.llu.edu/lbrand/research-bridger.html

http://www.rockymountainpaleontology.com/bridger