ABSTRACT
Joseph Silas Diller worked as a United States Geological Survey (USGS) geologist for some forty years, from 1883 to 1923. While his principal interest was in petrography, he was responsible for production of numerous geological maps, reconnaissance surveys and economic geologic studies. A majority of these were in Southern Cascadia, the complex region of southern Oregon and northern California that encompasses portions of the eastern Great Basin, Sierra Nevada, Cascade Volcanic, Great Valley, Klamath Mountains and Coast Ranges geologic provinces. Among his achievements were the production of six maps as part of the USGS Geologic Atlas Folio Series, in-depth reports on the evolution of Crater Lake and Lassen Peak, detailed descriptions of several mining districts, and the preparation of sets of hand specimens, thin sections and descriptions for colleges and universities. He was also a specialist on asbestos, coal, placer gold and chromic iron ore. He is perhaps best remembered for his studies of Crater Lake and analysis of Tertiary peneplanation and regional uplift. 
