Noah Hawley. A Conspiracy of Tall Men (1998) 295 pp.
Linus Owens teaches conspiracy theory at a college in San Rafael and lives in a house with a view of the Bay. He is told by federal agents that his wife has been killed in the company of another man when a bomb brings down a plane on flying from New York to Brazil. He and his two conspiracy buff best friends smell a rat and start trying to figure out what really happened. The search goes through Georgia, Chicago, Los Angeles, the four corners area, and Portland, but it starts from and returns a few times, to San Francisco. They have to track down mysterious anti-government crusaders, avoid various government agents, and sort out fact from fantasy while avoiding hired hit men and aggressive mental health professionals. It turns out it pays to be suspicious of government and big corporations.
Setting: San Francisco, San Rafael, etc.

P.B.