Archive for category Geology
Rise of the Ranges of Light: Landscapes and Change in the Mountains of California, by David Scott Gilligan, Heyday (www.heydaybooks.com), 2011, 209 pages, $18.95
Tectonic activity isn’t exactly an ice-breaker at a cocktail party, nor is it anything you’d expect to hear expounded on at a poetry reading. But that’s exactly what David Scott Gilligan has accomplished in Rise of the Ranges of Light, the sort of fortunate result of spontaneous generation you might expect if you left a copy of Outside Magazine, a geology primer, and Henry David Thoreau’s Walden in a dark corner, which when spawned unravels in a lyric, tectonic tale.
Although billed as a work of “natural history”, Gilligan’s opus to the genesis of California’s mountains is more accurately a “geological history” of the primal forces that painstakingly crafted the landscape we know today. Take for example California’s “mutt” geologic ancestry best seen along California’s coast, an accreted jumble of Sierran granitic crusts and tropical terranes stacked like congealed grease on the coastal spatula of North America. Or California’s paper-thin crust (12-19 miles thick), the result of the North American and Pacific plates pulling at each other like taffy, leading to the San Andreas Fault and the rerouting of mountain ranges.
Centering his expose on the Sierra Nevada, the range John Muir dubbed the “Range of Light”, Gilligan introduces the Sierra as being “one of the earth’s most extensive complexes of granite ever distilled from the earth’s mantle and emplaced in the crust”. Beginning with the batter churning deep below the earth’s crust, Gilligan patiently paints the process of mountain building that shouldered granite peaks like the Sierra Nevada into the heavens, a melange of spreading sea-floors, crumbling continental crusts, and mulling magma. What makes his writing so inviting, though, is his ability to conjure up these processes as if viewing the earth like a halved orange: the settling of the Central Valley and Great Basin caused by the sheer weight of a volcanic basement of granite overburdened by continental crust, or mountains “floating” in the continental crust like so many ice cubes in a glass of tapwater. When Gilligan describes the elastic, see-saw tension between mountains and the earth’s crust, it becomes all too apparent how a gardener (for example) barely scratches the earth’s surface moving a shovelful of garden soil, an act equivalent to throwing a soggy pea at an elephant compared to the tectonic forces at work.
For better or worse, the mountains of California are both hallmarks and harbingers of change. As sobering as it is imaginative, Gilligan’s prose brings the realities of the Sierra Nevada’s present plight to bear. Writing about global warming’s increasing influence above tree line, he laments:
“Everywhere I go the glaciers are dying… White spots on the map are reduced a hundredfold, now mere trimmings of once vast snowfields. It’s like returning to a beach to find that the sand has disapepared, taken away by tidal rips to some undefinable place-not moved or changed, but altogether gone… Trees seem to march upslope and young recruits are seen on high sites where no adults have been seen for a thousand years… The land has a thirsty feel that a winter or two of heavy snowfall can no longer slake.”
Gilligan’s writing betrays his passion for the mountain landscapes he has come to know so well, not only as a professor, but as a student of the wild, an avid naturalist, and a climber. If every geologist wrote with such passion, perhaps more Californians would abandon the shackles of Silicon Valley to become Shackletons of the High Sierra.