Almost got suckered into a VFR zero vis situation at altitude today. I was trying to make it back to Sonoma County from Pine Mountain Lake as I climbed up above the smoke layer at 6500. I had reasonable visibility of the ground - for about 15 minutes. As i got just south of Columbia Airport I could see for about 50 miles in either direction of the Sacramento Valley. It was a solid layer of smoke, with a clearly defined top around 6000 feet. No way i was flying over a solid layer of smoke with no guarantee of being able to get down at my destination. About the time I made this decision i looked down to see my vertical visibility was dropping. Unbeknownst to me another fire had started near Calaveras and was now adding to the smoke from the Ferguson fire and the other large fire off Hwy 108. About 25 years ago I almost lost control of an aircraft in smoke and have an inherent fear of it. This added to my anxiety as I immediarely turned towards my "out", Columbia Airport. Surprising, even as i descended at about 1000 fpm the vis was still dropping. This really amped up my anxiety. I'm a short 5 miles from the airport but the vis has dropped to maybe 2 to 3. At this particular moment i was glad i had turned on the 3d view on my IFly GPS. Having some idea of the terrain helped me to get in sight of the airport. My landing was horrible but i was friggen happy to be safe. I hate to think what could have happened if i delayed my decision to aim for Columbia, even for two more minutes. I called my wife who was still at Pine Mountain Lake. "Honey, I'm at Columbia Airport, can you come pick me up?". As i waited at Columbia I watched Calfire aircraft, land and take off about every 5 minutes. I have no idea how those heros fly in those conditions and worse, in mountainous terrain, all day long.