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COASTAL SOUTHERN CALIFORNIA is a semiarid land crosshatched with mountain chains, narrow valleys, and dry riverbeds. The upper reaches of its steeply sloped canyons are nearly impenetrable—its sunny broken rises blanketed with greasewood and sumac and mesquite, dense miserly plants that survive eight or ten rainless months each year. The shady slopes, turned away from the sun, are covered with oak and fern, and at higher elevations maple and big cone pine. On the flats and along streambeds grow sycamore and alder, their roots sunk deep into the loamy alluvial soil. In rare decades when one drought year follows another, stands of alder along dry creeks wither and die as groundwater falls away deeper and deeper into the earth.
But this parched landscape is largely a surface phenomenon, for beneath its plains and arroyos and rocky gullies lie vast aquifers of water-bearing rock. Unceasing and invisible cataracts flow beneath the dry beds of intermittent streams, and where strata of granite and basalt lie close to the surface, the water above is forced upward until it lies in quiet, leafy pools in the shaded canyons, even in the driest years. Elsewhere, almost as a counterpoint to these solitary pools, creek water tumbling down rock-strewn beds might vanish suddenly into the ground as if into a chasm, and within a few short yards, what had been a flowing stream over mossy stones and boulders is a desert of dry sand and rock, littered with broken limbs and fallen leaves, its scoured stones bleached white in the sun.
And then with winter rains the groundwater rises again, and dry springs bubble to life. In the wet years, once in a decade or two, long-vanished waterfalls abruptly reappear, coursing down sheer canyon walls and feeding creeks and streams that have grown overnight into deep torrents of rushing water. In the otherwise silent darkness of the canyons, one’s sleep is troubled by the water-muffled clatter of heavy boulders shifting and rolling in swollen streams. Unwary canyon residents awaken to find themselves hopelessly stranded: crossings washed out, footbridges undermined, narrow hillside roads swept utterly away, paths blocked by fallen trees.
And even on the plains below the mountains and in the hollows of grassy foothills, shallow, spring-fed pools arise in once-dry meadows, and water seeps into long-abandoned farmhouse wells like the revived ghosts of lost and despaired-of memories. …