Of the 15 species found, all are terrestrial and 5 are probably now limited to stream caves in the canyon as troglobites or disjunct populations of troglophiles. These 5 species probably descended from forest litter-inhabiting ancestors living near the caves during past glacial-pluvial climates. This 'life zone' lowering occurred most recently from 24 000 to 14 000 yr ago. When the forest retreated upwards at the beginning of the present interglacial (about 8000 yr ago), some of the litter invertebrates which had entered the caves were locally isolated in them when adjacent epigean populations went extinct. -from Author