Geology of the Portage Pass Area, Alaska

• Main Author: Barnes, Farrell F.
• Other Authors: Geological Survey (U.S.)
• Format: Report
• Language: English
• Published: United States. Government Printing Office. 1943
• Subjects: Geology > Alaska; Mines and mineral resources > Alaska; Geology; Mines and mineral resources; Narrow Neck; glaciers; Alaska
• Online Access: https://digital.library.unt.edu/ark:/67531/metadc944659/

Abstract: The Portage Pass area is in south-central Alaska, and includes part of the narrow neck of land that joins the Kenai Peninsula with the mainland to the north. This region is in general mountainous, elevations ranging from sea level to more than 4,000 feet on the peaks bordering the area. Several glaciers, all of which are apparently receding, extend into the area. Vegetation, chiefly alder and cottonwood on the valley lowlands and some spruce and hemlock on the lower slopes, extends to an elevation of about 1,000 feet, above which the slopes are bare except for occasional clumps of brush. The bedrock of the entire area is slate, argillite, and graywacke, apparently part of the same great series that extends from the Kenai Peninsula into the Prince William Sound region and is at least in part of Cretaceous age. The only igneous rocks recognized in the area are a few acidic dikes and a small diabase dike. Small, irregular quartz veinlets are widespread. The structure is not only complex but, owing to extensive metamorphism, is in many places obscure. A general northeast strike and steep to vertical dips of both bedding and cleavage planes are the rule, but there appears to be some broad folding along steeply northeast-pitching axes. Although no large faults have been recognized, much movement has occurred along many small faults, shear zones, and bedding planes. All observed faults and shear zones trend northeastward. There are no mines in this area. Some mineralization of quartz veins was noted at a few places, and some prospecting has been done, but no workable deposits are known.