It's incredibly funny...

An awful cheapo trend in filmmaking. So many movies supposedly taking place in Montana, Colorado, etc., were filmed in the rolling oak country of Southern California, to the utter insult of intelligent, informed viewers. Yes, there have been notable exceptions even in Oregon with on-location shooting. But it doesn't make up for the other - Bonanza episodes "on the Ponderosa" shot in the same old boring over-familiar So. California locations. The Planet of the Apes' greatest flaw was trying to substitute So. Calif. for Ape World. The Here Come the Brides TV show attempted to substitute the Columbia Ranch and the "Gidget beach berm" for frontier Seattle ... etc., etc. There is no substitute for location shooting. Only historical movies that depict So. Calif. history should be filmed in that overused location!

Yep, but it's still a beautiful lake. Maybe this location was more convenient for them :-)