For the most part the Reconquista folks are terminally stupid. Let's say we pulled out of that territory ~ and took our water with us!
Which, BTW, is very doable. There'd be 20 million people South of I70 with nothing to drink.
Worth remembering ~ the Russian claim starts somewhere in the San Francisco region and includes all the water courses back to the headwaters of the rivers draining into San Francisco Bay.
We acquired the Russian claim through the simple expedient of occupying California ~ the Russian claim, of course, had been on top of an earlier British claim that had not been exercised by UK.
It is arguable that Northern California was sufficiently separate from California to constitute territory not claimable by Mexico based on extension of claims made by Spain.
California is NOTHING without Northern California's water. Aztlan is a burning, nasty desert without Northern California's water.
Oh hell, we don't have to ever feel bad about the Spaniard claim. It was based on the Treaty of Tordesillas and the Pope gave them everything to the North Pole. It was utterly silly and the people in Europe at the time thought so too: especially us Protestants in England and Germany. California was land they never had and never held, which is why it fell so quickly to Stockton and Fremont.
As for denial of resources to the newly occupied Aztlan, don't forget where the electric power for California really comes from, and ask yourself if the Governors of the Western States should pay attention to things like the interstate water compacts negotiated and agreed to long ago when the population of California was not predominantly foreign.