Volcanic tuff beds of the Mint Canyon formation

Abstract

The Mint Canyon formation (Upper Miocene) consists of a series of continental sediments including both fanglomerates and fresh-water lake deposits. The basin of deposition of the lake sediments was near the sea but was apparently definitely separated from it. Some 4000 or more feet of sediments have accumulated. The Mint Canyon formation lies nonconformably above the Vasquez formation (Oligocene?). The angular discordance between the Mint Canyon formation and the overlying Modelo (Upper Miocene) is not great but is definite in many places. A series of volcanic tuff beds are present in the Mint Canyon formation. There are at least 8 major tuff beds and possibly as many as 5 minor ones. Individual beds reach a thickness of 10 feet. The tuff, for the most part is a fine grained, acid, vitric tuff, though some crystal fragments are present in certain units. Others are contaminated by sand and grit. There is some suggestion that the pryroclastic material has been derived from the Mojave Desert area and is possibly from the same source as the rhyolitic material of the Rosamond formation. The outcrops of the tuff are restricted to two main areas, one on either flank of a broad, westerly-pitching syncline which is the major structural feature of the Mint Canyon area. In each of these areas, local sections of overturning are present. It is believed that these are the surface manifestations of faulting in the basement complex. Faulting is present to a moderate degree. The major faults are probably steep with vertical movement being most important. Plant fossils are preserved in the fine tuffs. The flora indicates a biseasonal distribution of rainfall with possibly slightly greater annual average than at present. The Mint Canyon flora is part of the Mojave floral province. Fine grained units of the tuffs are quarried and used to a limited extent as surfacing material on asphalt shingles and roofing material.