The original purpose of this study was a detailed structural analysis of the Jurassic Otter Point Formation in order to determine if the Canyonville Fault Zone, which forms the northern boundary of the Klamath Mountains in the Riddle - Canyonville area (Benson and Perttu, 1980), extends westward to the coast and, if possible, to characterize the structure of the Otter Point Formation. Further, a detailed examination of the structural and stratigraphic relationships between the Otter Point Formation and the Eocene Roseburg and Lookingglass Formations was to be performed in an attempt to determine the tectonic history of the area.

A computer technique for interpreting geophysical logs of drill-holes in quantitative lithologic terms has been developed and tested on the deposits of the late Eocene Coaledo Formation, a well-studied fluvio-deltaic complex in southwestern Oregon. The technique involves the use of induced and natural gamma logs for separation of coal and claystone from coarse-grained detrital rocks and the use of the ratio of resistivity and natural gamma responses (defined here as the "grain size index") to divide the coarse elastic rocks into a series of textural classes corresponding to the Wentworth-Odden particle size scale.