When I was at the Oregon 40th HG anniversary meet at Cape Kiwanda Dave Raybourne told me that the cliff soaring pilots back in the day had a theory that thermals wouldn't form inland over the dark, dense, forest, so they stayed on the cliff to soar. Even though they knew that sailplanes had been using thermals inland they thought it had something to do with them being farther from the coast, or something like that. They also didn't know there could be thermals over the ocean.
When I started producing my varios those guys started launching in the cliff slope lift and then doing long cross country flights by finding thermals over the coastal forests, now that they had a very sensitive (much more sensitive than the sailplane varios in use then) way to know when they were gaining altitude. He told me that one guy flew completely across the city of Portland, using the Colver vario, way back then. However, I don't remember if that guy launched at the coast or some inland site. Portland is quite a distance from the coast.
Man! I can't imagine depending on thermals to cross a dense city like Portland. I wonder how many potential roof top landing areas he looked at? As I recall, the parks are all full of big trees.
Frank