What would the effects on climate in the western United States be if Death Valley were an inland sea connected to the Gulf of Cortez?

Answer 1

Probably not a lot. The climate of the West is generally dominated by large high pressure areas that are due to global-scale circulation. Adding more moisture at the surface isn't going to change the fact that dry air is descending over the region, which pretty well cuts off vertical development. Look at places where there is an arm of the sea reaching into a desert region: the Red Sea and the Persian Gulf are the best examples. Right on the eastern shore there are very hot and humid microclimates, but you don't have to get too far away for it to go right back to being a regular desert again.