The Latah Formation in Idaho

Abstract

It has been known for about thirty-five years that a fossil-bearing sedimentary series is interstratified with the Columbia River basalt throughout eastern Washington and northern Idaho. It has been observed and described in print by several geologists of the United States Geological Survey, as well as by workers on state surveys. In 1926, it was named the Latah formation in the Spokane area by Pardee and Bryan. Fossils collected by the writers from Russell's localities and from many new stations make certain that the Idaho localities represent exposures of the Latah series. In Idaho, usually two or more layers occur separated by basalt flows. This offers persuasive evidence that the Latah is a series, rather than a formation. Although the lake beds are believed to be of local origin, and comparatively disconnected, the area in which outcrops occur is approximately 175 miles long and 75 miles wide. The type locality, near Spokane, appears to be abnormal when its characteristics are compared with those of a large number of the widely distributed Idaho localities. This article is the result of only a preliminary study, and future work will no doubt yield new localities and more complete collections of the flora.