Microscopic studies of well samples from the Uinta basin, Utah, indicate that deposition of the Green River formation occurred in a dominantly lacustrine environment which graded laterally toward the margins of the basin into fluvial environmental phases. The paleogeography of "Lake Uinta" in Utah is divisible into three main events: a major transgressive stage, a period of stability, and a major regressive stage which ended Green River lacustrine deposition in the Uinta basin.

A newly named stratigraphic unit at the base of the Green River formation, here called the "black shale facies," represents the oldest rocks assigned to the Green River formation in the Uinta basin. The Green River-Wasatch formational contact is a transgressional plane. The lithologic character, general paleontologic content, geographic extent, environment of deposition, and age relationships of the units are discussed.

The delta facies of Bradley is used in this paper in a slightly expanded manner.

The Parachute Creek and Evacuation Creek members contain the sedimentary record of an essentially stable period, and tuff beds found in the members indicate their time-equivalence across the Uinta basin.

The saline and the sandstone and limestone facies were deposited during the major regressive stage ending Green River sedimentation. The two units are time equivalents of part of the Uinta formation in the subsurface and Dane assigns them to the Uinta formation on the basis of surface mapping.

The lacustrine sediments of the Green River formation in the Uinta basin are described.