I think a large Canal would be the best bet, then let the valley flood until it matches the Pacific, if engineered correctly this could be an actual inland sea/port which would be used by California (and Mexico-a small sliver being on their Mexicali).
It could be used for 1) Inland Naval Base (if a canal were created wide enough for naval vessels and commercial container craft, among others such as luxury yachts and fishing vessels.
2) Desalization plants could be constructed along part of the shore.
3) Recreactional fishing/watersports in this new “sea”.
4) New shoreline for luxury homes
5) New shoreline for waterfoul and other natural habitat.
Of course this would have to be created in partnership with Mexico as it would require a new treaty.
Come on man! It's a f***ing desert... there is no fresh water and barren, toxic soil. To build there is an irresponsible waste of resources... that these days are ALL funded by the taxpayers.