Geology of the Mint Canyon area, Los Angeles County, California
Creators: name: Holser, William Thomas
Publisher: name: California Institute of Technology
Year: 1946
Subjects: subject: Geology
subject: FOS: Earth and related environmental sciences

description: The area described covers approximately ten square miles
in the Lang and Humphreys quadrangles, twenty-seven miles northwest of Pasadena. It comprises part of the drainage of Mint Canyon immediately southeast of the area previously described by R. H. Jahns, and continues eastward across Tick Canyon, west of an area previously described by R. P. Sharp.

A series of pre-Cretaceous gneisses outcrops in the northern part of the area as an uplifted fault block. Immediately to the south of the fault lies the Vasquez series, of doubtful Oligocene age. In this area, it is composed of two sections of coarse, colorful sandstones and gypsiferous shales, alternated with two thick flows of basaltic lava, the total thickness being about 3000 feet. Unconformably overlying the upper lava flow is the Miocene series. This series was deposited in a broad basin. The initial basinward dips have been accentuated by slight folding at a later date. The lower part of this series was named the Tick Canyon formation by Jahns. He described a section west of Mint Canyon, unconformably resting on the basin complex, which pinched out eastward. In this paper, the Tick Canyon formation is described from a section
measured in Tick Canyon. The map shows that it does not entirely disappear at any point, east of Jahns' area, except where it is cut off by a series of strike slip cross faults. The Tick Canyon formation is principally composed of green sandstones, reddish siltstones, and some conglomerates, with a total thickness of over 1000 feet. Overlying the Tick Canyon formation is the Mint Canyon formation; however, no clear evidence could be found in this area for an unconformity between the two formations, as reported by Jahns. The Mint Canyon formation is composed of continental deposits: light colored pebble to boulder conglomerates roughly interbedded with light sandstones and reddish siltstones. The total thickness of the Mint Canyon formation outcropping in the area mapped is about 3500 feet. The section is thicker than that in the area mapped by Jahns, possibly because it received coarser sediments more rapidly near the margin of the basin. A Pleistocene erosion surface, with accompanying terraces is shown on a separate map.

There is a normal fault of large but unknown displacement between the Tertiary sediments and the metamorphic complex. Several branches of this fault run into the sediments, but gradually die out to the southwest in the Mint Canyon formation. The largest branch, which causes a considerable horizontal displacement of the sediments at its northern end (west of Mint Canyon), gradually decreases in displacement to the southwest where it passes into an anticline. There are a number of northwest trending, normal, cross faults of relatively minor importance. Accelerated uplift of the San Gabriel mountains in late Miocene time is indicated by the increasing dominance of San Gabriel intrusive material in the upper members of the Mint Canyon formation. Middle Pleistocene uplift of the whole area is indicated by the stream terraces, but there is no evidence of recent faulting in this particular area.