Since you mention Yosemite, April is a fine time of year there too, except that the high country isn't open yet (but most times of year that the high country is open, the valley is very crowded, so you can't have everything).
As someone mentioned, highway 120 into Yosemite from the east is closed for the winter; you have to drive somewhat north through Lake Tahoe or south around the south end of the Sierras, and come into Yosemite from the west that time of year.
Lisa