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Bruce Ueno's Blog

Tin Mine Canyon, Santa Ana Mountains, California

27th Nov 2011

Over the Thanksgiving holiday, we took some time to explore the intriguingly named Tin Mine Canyon area of the Santa Ana mountains, virtually walking distance from my home, on reports of a find of schorl. Our search proved fruitless on this occasion, but the expedition did reveal a few items of historical and geological interest which we share here.

The Santa Ana mountains are relatively diminutive as mountain ranges go, reaching a maximum height of 5687 feet above sea level at Santiago Peak. Collectively, the many low summits form the northern terminus of the peninsular ranges, in the same geomorphic province as the famous gem districts of San Diego to the south. While gem pegmatites are unknown as far northward as the Santa Anas, schorl had historically been found at the nearby Cajalco tin mine, and at the Santa Ana mine at Trabuco canyon.

At the mouth of the canyon, the northern wall (right-hand side of the canyon) consists of Baker Canyon Conglomerate, a formation composed primarily of marine sediments with localized clastic igneous deposits. Thin beds of fossiliferous standstone within the formation contain clam shells in abundance, though these tend to be of poor quality and well-cemented within the sandstone and therefore not particularly collection-worthy. Some of this material can be seen along the roadway, where it has tumbled from the canyon wall.

Faulting in the Bedford Canyon Formation, Santa Ana Mountains

Santa Ana Mines, Trabuco Canyon [town], Santa Ana Mts, Orange Co., California, USA

Further into the canyon lies the Bedford Canyon formation, which contains beds of lightly metamorphosed sandstone, graywacke, quartzite, slate and argillite. This formation comprises the basement rock of the northern range, and it is from this strata that the commercial extraction of tin and other minerals in the Santa Anas was attempted. One of the more notable efforts occurred in the early 1900's when a promising find in Trabuco Canyon, on the opposite, southern slope of the range, created a local boom. It was there that the Santa Ana Tin Mine was incorporated and a mine and mill constructed. The enterprise was backed by New York businessman Gail Borden III, the inventor of condensed milk, who needed tin for his dairy operations. After a princely sum was invested into the project, the mine was ultimately abandoned as unprofitable- the deposits proved to be of low quality, and the Bedford Canyon formation too fragmented for productive veins to be traced. The old claims at Tin Mine Canyon remain as testiments to this short-lived boom era.

Mine Entrance, Tin Mine Canyon, Santa Ana Mountains, CA

Santa Ana Mines, Trabuco Canyon [town], Santa Ana Mts, Orange Co., California, USA

Although a number of exploratory shafts can be still be seen in Tin Mine Canyon, none proved to be commercially viable. Today their stark and silent adits serve as a reminder of the dreams of a bygone era of prospectors.

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