This Land 



Traverse Creek, California 



by Robert H. Mohlenbrock 



Originating in the foothills of Califor- 

 nia's Sierra Nevada Mountains, rocky-bot- 

 tomed Traverse Creek descends south for 

 more than a inile through a tree-covered 

 canyon and then passes gently through the 

 middle of a shallow basin. The basin, 

 carved out by the creek in ages past, is 

 only slightly lower than the neighboring, 

 flat terrain, but it is easily distinguished by 

 what grows there. Surrounded by a dense, 

 green forest of ponderosa pine, Douglas 

 fir, and incense cedar, the basin itself con- 

 tains only shrubs and a scattering of digger 

 pines — often multitrunked trees with 

 large, heavy cones and long, pendulous, 

 gray-green needles. Because of its unusual 

 vegetation, the basin's 200 acres are man- 

 aged as a botanical special interest area by 

 the Eldorado National Forest. 



As I learned from forest botanists Mike 

 Foster and Mark Williams, digger pine 

 grows in the basin, and ponderosa pine, 

 Douglas fir, and incense cedar do not be- 

 cause Traverse Creek is adjacent to de- 

 posits and rock outcrops made of the min- 

 eral serpentine. Geologists believe that 

 serpentine rock, or serpentinite (named for 



Pine cones rest at the base of a digger 

 pine, above. Right: Bitterroot grows 

 in arid liabitats. 



Thomas Hallstein: Outsight 



68 Natural History 2/94 



its undulating, layered texture and mottled 

 coloring), was first exposed in California 

 about 150 million years ago. Today it is 

 common enough to be California's state 

 rock, covering many discontinuous areas 

 for a total of about 1 , 1 00 square miles. It is 

 most common in the South Coast Range, 

 the North Coast Range, the Bay area, and 

 the western foothills of the Sierras. 



The soil that forms when serpentine 

 rock weathers is so low in some of the ele- 

 ments plants depend on — calcium, potas- 

 sium, and even the molybdenum needed in 

 trace amounts — that most plants can't sur- 

 vive in it. In addition, the soil is unusually 

 high in nickel, cobalt, chromium, and 

 magnesium, which are toxic to most 

 plants. As a result, serpentine soils usually 

 have a sparse cover of plants that can ex- 

 tract the minerals they need while coping 

 with the toxic chemicals. For example, a 

 wild mustard known as milkwort jew- 

 elflower, which grows only near Traverse 

 Creek, can take up nickel in excess of 

 1,000 parts per million without any appar- 

 ent harm. Other serpentine species of jew- 

 elflower and many other serpentine-toler- 

 ant plants take up nickel in modest 

 amounts or exclude it altogether. Plants 

 not found on serpentine soil, including 

 some species of jewelflower, may die in 

 soils containing only a few parts per mil- 

 lion of nickel. 



Arthur Kruckeberg, an authority on the 

 botany of serpentine areas, notes that the 

 vegetation in such relatively arid locales as 

 Traverse Creek is made up of chaparral 

 with a sprinkling of digger pines. In the 

 Traverse Creek basin, the chaparral con- 

 sists of four- to eight-foot-tall bushy 

 shrubs, including four species in the buck- 

 thorn family — buckbrush, deerbrush, Cal- 

 ifornia coffeebush, and red inkberry — as 

 well as leather oak and white manzanita. 

 Most of these shrubs bloom in May. The 

 manzanita is notable for bearing its littie, 

 white, bell-shaped flowers at the tips of 

 very sticky stalks. The stalks impede ants 

 that might crawl to the flower in search of 

 a pollen meal: instead, the pollen is re- 

 served for the flying insects that pollinate 

 the plants. 



