2 D3. Advances in Geoarchaeology

Monday, 26 October 2020
1:30 PM - 5:30 PM
Meeting Rooms

HOW STAGECOACH DRIVERS NEGOTIATED VERY STEEP GRADES DURING THE LATE 1800'S, SLIPPERY ROCK ROUTE, SANTA BARBARA, CALIFORNIA

Paper number: 2-8
Program: Technical Sessions
Time: 3:05 PM – 3:20 PM

Authors

Abstract

Slippery Rock is a portion of a stagecoach route that functioned between Santa Barbara and Santa Ynez, California, and for twenty years represented the only northward overland route from Santa Barbara, California. The stagecoach line was operated for 40 years, between 1861 and 1901 (Tompkins, 1982, p. 11). An assessment of their grooves worn into the sandstone rock in conjunction with steep grades in excess of 20 percent, indicates the groves were deepened by drivers locking the wagon rear wheels as the stagecoaches descends rocky slopes of up to 23.6 percent grades. The depth of the grooves steady declines from 1.2 feet until zero to within 30 feet of the bottom of the sandstone indicating wheels were unlocked and the 50 long wagon train attained purchase on the nearly flat soils beneath the sandstone.

A four foot long hand held digital level and tape measure were used to measure slope grades, lengths, and depth of incision of the groves into the Oligocene Sespe formation sandstones and conglomerates. A 25 foot sample interval was used along most of the survey for a total length of 450 feet. The old stagecoach route crossed the sandstone dip slope at an elevation of 1,200 feet above seal level. In most cases the maximum depth of the groves coincides with the steepest grade of the route. The grooves were initially carved to a depth of 0.25 feet to keep the stagecoach steady while traversing the sandstone, according to Tompkins (1982, p. 31). The grooves deepened while locking the wheels over time, and became destructive to the wood spokes on the stagecoach wheels, according to Tompkins. Each stagecoach that carried passengers were pulled by six horses, arranged two abreast, which comprised length of stagecoach and horses of about 50 feet, based on historical photography.

The groves were measured to be rectangular in shape with flat bottoms. The grooves were found not to be deepened by subsequent erosion during the 118 years since their development. Lack of erosion is indicated by presence of quartzite clasts at a depth uniform to the surrounding sandstone matrix, and the clasts have metal flakes stuck to them from the metal rimmed wagon wheels.

Geological Society of America Abstracts with Programs. Vol. 52, No. 6

doi: 10.1130/abs/2020AM-355562

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