• Retallack et al. (2000): Near-shore, shallow-marine environments are indicated by sedimentary structures such as hummocky cross-bedding, shallow water trace fossils such as Planolites and Thalassinoides and common glauconite and phosphate nodules (Mears, 1989).

•Hickman (1969): Several lines of evidence suggest that most of the Eugene Formation was deposited in shallow water, at depths no greater than 30 fathoms. The coarse, tuffaceous, and arkosic character of many beds and the interfingering of the Eugene Formation with non-marine tuffaceous rocks to the east and south indicates the proximity of the Oligocene shoreline. Although mollusks are generally not good indicators of depth, genera such as Panopea, Modiolus, Solen, and Spisula are presently restricted to depths of less than 40 fathoms. The high diversity of the benthonic fauna is an indication that the environment was not one of a bay or otherwise highly restricted environment. The absence of planktonic forms is typical of turbid, near-short environments. In the same units with these relatively undisturbed infauna! assemblages there are occasional thin layers of concentrated shell material which show definite signs of reworking and current sorting. The layers range from 1 to 10 cm in thickness and cannot be traced over great distances. The shells in these layers are small and include an admixture of infaunal and epifaunal species. The shells show little sign of wear or breakage, but many of the pelecypod valves are disarticulated, indicating some degree of transport. The scaphopods in these layers show parallel alignment by the current. There is also evidence that currents were intermittent and fluctuating in strength: the assemblages contain varying percentages of large shells mixed in with the smaller ones, and in some places there are higher proportions of broken and abraded shell debris mixed in.

• Tuffaceous and highly feldspathic sandstone or siltstone which is bluish-gray to olive when fresh and weathers to a buff or orange-brown color. Gray sandstone and siltstone beds may range from several to 50 feet in thickness and are interbedded with minor amounts of sandy sahel and clay shale, occasional beds of conglomerate, and thin lenses of gray or buff-colored volcanic ash