Mono Pass and Ruby Lake in October.  My wife, Debbie, and I took a long trip to the Four Corners area but on the way we did a three night backpacking trip in the Sierras from Mosquito Flat to Ruby Lake and then day hiked the area, including Mono Pass (~12,000')   Saw very few people, no bugs, and cold mornings.  This is a very popular trail, and for good reason.  It's beautiful and easy.