Possible active fault traces on or near the Castle Mountain fault between Houston and the Hatcher Pass Road: A section in RGeologic studies in Alaska by the U.S. Geological Survey, 1993

The Castle Mountain fault is one of several major east-northeast-striking faults in southern Alaska, and it has had historical seismicity and Holocene surface faulting. The Castle Mountain fault was delineated on a regional scale by Detterman and others (1974, 1976), who divided it into two physiographic segments. Mapping in a 30-km-long region between the two segments (from Houston to the Hatcher Pass Road) is the subject of this study. I found two faults in the central part of the study area, north of the inferred trace of the Castle Mountain fault, which have experienced late Quaternary surface-faulting. I also traced the Castle Mountain fault in the Houston area about 3 km farther east than previously recognized. The age of faulting in the study area is constrained by the glacial history to be younger than approximately 10,000 yr B.P. on several faults and younger than approximately 40,000 yr B.P. on another fault. However, because prior work on the Castle Mountain fault west of the study area has recognized surface faulting younger than 1,860 yr B.P., it is likely that the age of faulting within the study area is substantially younger than 10,000 or 40,000 yr B.P.