The best way to describe Doug Sahm's music is simply that it is Doug Sahm music: a mix of rock, blues, polka, country, swing, tex mex, a bit of jazz and psychedelia, lots of soul. Sahm was from San Antonio, Texas but spent a few years in the late '60s around San Francisco. Maybe you have heard his songs "Mendocino" or "Sunday Sunny Mill Valley Groove Day." If you want to check out some of his music I would suggest "Best of Doug Sahm and the Sir Douglas Quintet 1968-1975", "Doug Sahm and Band" and "Groovers Paradise."
Below you can see a video clip of Sahm on Austin City Limits performing "She's About a Mover."