The problem is that anywhere at altitude is likely to be snowy, and then anywhere on the coast from central California north is quite likely wet. That leaves the southwest deserts and southern California, and even then only those places (essentially southern Arizona, Nevada and southern California) that are not that far above sea level and therefore not too cold. Death Valley, being below sea level, is perfect.
Relief map of the western US.
Otherwise, there's a reason Americans go to Mexico, the Caribbean or Florida for spring break...