Dillon is what another generation would have called an antiquarian -- librarian of a California historical collection, and author of half a dozen books about odd bits of pioneer history. Siskiyou Trail -- twelfth of The American Trail Series -- uses diaries, correspondence, and other records from the 1820's to the 1840's to reconstruct the opening of a route between British-occupied Fort Vancouver (now Vancouver, Wash.) and Mexican-ruled California. This occurred chiefly under the aegis of the Hudson's Bay Company, which hoped to extend fur-trapping activities south into California, sidestepping the weak authority of Mexico before the U.S. moved into the vacuum. After repeated painful treks through the daunting terrain of the present Oregon-California border, a route was established through the Siskiyou Mountains straddling the two states; although the poor beaver hunting never justified the effort, the trail became a major avenue between Oregon and California during the Gold Rush (it's now U.S. 5). Filled with odd characters including botanist David Douglas (discoverer of the Douglas fir), assorted Iroquois (who assisted the Hudson's Bay Company in Western exploration), Canadian trappers, and American explorers (notably dumber than the British in their encounters with the Indians), this neglected scrap of Western lore has the makings of a rattling good narrative, but Dillon fails to bring much rattle to it. He has a peculiarly wooden touch with character, and his account plods along incident by incident, with little attempt at interpretation in any larger historical context -- not that larger contexts are indispensable to all historical writing, but Dillon lacks a coherent organizing principle for a multiplicity of events. The publishers plan an endpaper map (without which Easterners may have trouble following the sequence of travels). Disappointing.