A Range of Opinion

…or, perhaps, when engineers and geologists collide. (This is one of those little episodes GG had pulled up for possible inclusion in his book The Mountains that Remade America only to find it something of an orphan).

In 1863, the Big Four responsible for construction of the Central Pacific Railroad were in desperate need of funds. The 1862 Pacific Railroad bill allowed $48,000/mile to be loaned once the railroad entered the Sierra Nevada but only $16,000/mile before then. Up to 150 miles of mountainous terrain could be claimed.  Eager to get the most money possible, Charles Crocker got the state geologist, Josiah Whitney, to go on a buggy ride to decide where the western edge of the range might be. Whitney allowed that the Sacramento River might be the most appropriate spot, but both he and Crocker could see the terrain was quite flat.  So they rode off some 6 or 7 miles east to Arcade Creek where some reddish sedimentary rock was exposed, and Whitney allowed that this was an appropriate spot to claim the edge of the range. But when Theodore Judah, who was director of the line and was responsible for identifying the route and who had shepherded the 1862 bill through Congress heard, he was appalled. This was 21 miles west of where the line would encounter its first real grades.

This episode is widely derided as Whitney engaging in deception to aid the railroad.  Was this another example of Josiah being a total ninny, as when he accepted the Calaveras Man claims, or when he said there had never been glaciers in Yosemite Valley?

SacramentoGeol

Detail of Wagner et al., 1981, Geologic map of the Sacramento quadrangle, California, 1:250,000.

On the map above, the Sacramento River is at the left and the edges of crystalline rock of the Sierra is at the right. The Central Pacific runs under the “r” in the Arcade Creek label. The orange patterned unit on the map is the Turlock Lake Formation.  According to Unruh (1991), the 0.6 Ma Turlock Lake is tilted 0.19° to the west. For a geologist, this western edge of tilted and eroded Tertiary and Quaternary rock is indeed the most likely spot to mark the edge of the range. (Geologists today would not go along with the Sacramento River as the edge as its floodplain extends well east of Sacramento).

Whitney had, in fact, chosen a perfectly appropriate spot even though it was one that Stanford and Crocker had decided upon by measuring backwards 150 miles from the Truckee Meadows on the east side of the range. That this was not the essence of “mountains” as envisioned by an engineer like Judah was not Whitney’s fault; indeed, had the bill been written to assure that only truly mountainous terrain be included, Judah should have inserted minimum railroad grades or some other direct measure.

Whitney’s written acceptance of the Arcade Creek edge to the Sierra was seconded by two government surveyors in California and sent on to Washington, where Abraham Lincoln agreed that this was the appropriate point for the mountains to start. The Central Pacific got their higher loans earlier, but more through the ambiguity of the original legislation than deliberate misrepresentation on the part of the state geologist.

 

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  1. Mountains that Remade America | The Grumpy Geophysicist - April 20, 2017

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