| The geologic investigation and mapping of five 15-minute quadrangles embodying about 1,040 square miles within a radius of 25 miles of Portland, Oregon, are the basis for this report. The study has resulted in redefinition of the basic stratigraphy of the area, has yielded data on the nature of laterization and the time required for the formation of several profiles of weathering -- including fully developed laterite -- and has permitted a fuller understanding of late Quaternary history related to flooding of this area. A previously unknown laterite horizon was discovered during the geological investigation. -- Trimble, 1963 |
