The Geologic History of the Diamond Lake Area

This report is divided into three principal sections. The first, "Principles of Volcanic Activity", is designed to provide the layman with the background necessary to understand the geologic evolution of volcanic terrain such as the Diamond Lake area embraces. The growth and characteristics of volcanoes are described in non-technical jargon, and a minimum of technical geologic terms is introduced.

The second section of the report is "General Geologic Setting of the Cascade Region". This section describes the evolution of the Cascade Region, in general, and is presented merely to provide a broad geologic framework within which the Diamond Lake area may be placed. Also, a brief discussion of geologic time is included, and the terminology applied to the various divisions of geologic time have been introduced. This section may be understood by those possessing very little geologic knowledge, and by persons with no geologic training whatever, beyond an understanding of the material presented in the first section.

Vicinity Map. Diamond Lake Area, Umpqua National Forest.

The third section of the report describes the geologic evolution of the Diamond Lake area. For purposes of this report, the phrase "Diamond Lake area" refers to the Diamond Lake Ranger District of the Umpqua National Forest. The geologic map (see in side back cover) covers approximately this area. The geology of areas outside this district is discussed where geological phenomena in those areas influence the geological development within the Diamond Lake area or, conversely, where the influence of geologic phenomena within the Diamond Lake area is felt in other areas. This section, dealing with the geologic history of the Diamond Lake area, is designed to be understood with no more geologic knowledge than that available in the first two sections. Anyone with a modicum of geologic training will be able to read the third section without digesting the previous two, though he might find the second section of general interest in the way of background material.

The geology of the Diamond Lake area has not yet been thoroughly mapped or investigated. The brief period the author spent in the area (mid-June to mid-September 1963) revealed the numerous technical problems that await resolution. However, it is hoped the information contained in the report will provoke a greater appreciation of the area by the reader.

Reconnaissance Geologic Map and Geological Cross Sections of the Diamond Lake Area, Umpqua National Forest, Oregon. (click on image for a PDF version)