 He found that the trees most exposed produced the most precipitation and in five weeks of measurement (July 20-August 28, 1951) fog drip below the tanoak produced 59 inches of precipitation, more than the total annual precipitation on nearby grasslands and chaparral.The Douglas fir produced 7-17 inches of fog drip and appeared to provide unique conditions supporting the orchids giant helleborine ("Epipactis gigantea") and phantom orchid ("Cephalanthera austiniae"), since these plants were found exclusively in these moist ridge tops.The upper reach of the lower watershed of San Mateo Creek below Crystal Springs Dam consists of open space and sparsely developed residential areas of the cities of Hillsborough and San Mateo, California.