Songfacts®:

• Mendocino is a small vacation town on the coast of California. The song was written by group leader Doug Sahm, who was living about 250 miles away in Prunedale, California at the time. According so Sahm's son Shandon (Doug died in 1999), this song was inspired by a vacation Doug took to Mendocino with a lady from his record company.
• The Sir Douglas Quintet came on the scene in 1965 with their first single, "She's About A Mover." They were from Texas, but tried to pass off as Brits to tie in with the British Invasion bands that were huge at the time (thus the band name). That ruse didn't last long, but in 1968 they became a California hippie band, albeit with a Tex-Mex sound. "Mendocino" introduced this new look and got them back on the chart. It was their last substantial hit, but the group proved very prolific, with a string of recordings typically in the roots music genre. The Sir Douglas Quintet folded in the mid-'70s, but Doug Sahm carried on as a solo artist, and later with the group The Texas Tornados.
• Sahm does a spoken intro at the beginning of this song:
  
  Sir Douglas Quintet is back. We'd like to thank all our beautiful friends all over the country, and all the beautiful vibrations. We love you.
  
  It's a very peace-and-love sentiment welcomed by the hippie crowd.