Thursday, June 22, 2006
They're not just rocks, they're history -- A guide to the Sierra Nevada's geology
By DAN BARNETT
Three decades ago geologist Mary Hill wrote a handbook to the Sierra Nevada's geologic history and it became the standard guide. The aptly named author has now extensively revised her book. It's an armchair traveler's delight and remains an authoritative guide that will well serve a new generation of hikers, campers, and explorers.
"Geology of the Sierra Nevada: Revised Edition" ($19.95 in full-color paperback from University of California Press) contains almost 200 illustrations, including photographs of rock forms and maps showing where to find them. Hill thanks Bill Guyton, professor emeritus of geosciences at Chico State University, "for his careful reading" of the new manuscript and draws on the research he published in "Glaciers of California" (1998). Guyton distinguished between glaciers and smaller "glacierets" and counted 99 glaciers in the Sierra Nevada and 398 glacierets. Hill notes that "the Sierra Nevada has a lot of glaciers, all of them small. If you are looking for the giants of the Great Ice Age, you will have to be content with their spoor."
The book is divided into two sections. The first offers a "do-it-yourself rock identification key." A series of maps divides the Sierra Nevada into regions and shows where to find prominent rock formations in each area. The first map, mostly of eastern Butte County, locates "conglomerate" ("rock ... made up of grains 2 mm or more in diameter, together with coarser fragments") along Big Chico Creek. You can see shale in the Dry Creek area and lava flow and basalt on Table Mountain.
The second part is the narrative, which takes new research into account. In the last few years, she writes, "the Sierra has been put through the plate tectonics intellectual filter, which has told us how the mountains might have been created, and why they are where they are."
The book also expands its coverage of "human exploration of the Sierra Nevada, not just by geologists" but by others as well.
Here you'll find the story of "the first overland party of settlers to attempt to cross the Sierra. ... The group came to be known as the Bartleson-Bidwell party, as it included two men of leadership mold, John Bartleson and John Bidwell, destined to become eminent in what was to be the 31st U.S. state." Here also is the story of "Snowshoe" Thompson, a Norwegian who for two decades, "beginning in 1856, ... carried the mail across the Sierra Nevada from Placerville, California, to Genoa, Nevada (then called Mormon Station), using long skis (then called 'snowshoes') of his own making."
But Hill's great love is the land itself, the "nervous" Sierra, and her account of the devastating Owens Valley earthquake in 1872 tells not only of human destruction but notes that "the Sierra Nevada itself was severely wracked." She quotes John Muir's eyewitness account: "Shortly after sunrise a low, blunt, muffled rumbling, like a distant thunder, was followed by another series of shocks, which ... made the cliffs and domes tremble like jelly, and the big pines and oaks thrill and swish and wave their branches with startling effect."
At the end of the book, a "coda" reflects on geologic time and human time. "Time is all we have," she writes, "and it behooves us to spend it wisely. Some say that the time spent in the mountains is not subtracted from our allotted three-score-and-ten. So cherish the Sierra, and it will generously reward you."
Dan Barnett teaches philosophy at Butte College. To submit review copies of published books, please send e-mail to email@example.com. Copyright 2006 Chico Enterprise-Record. Used by permission.