Night is falling on the northern Sea of Cortez. It is eerily still. The terns and pelicans have gone to roost, and the dolphins no longer crisscross the water by the hundreds. The sea lions have hauled out for the evening. The usually temperamental water, the color of chocolate milk, is smooth as glass. Sundown is the best time to be on the upper Gulf of California, as the sea is also known, wedged against the Mexican desert, close to the U.S. border. The searing sun gives way to fantastic swaths of oranges, pinks and reds, painting the water with dancing shimmers of failing light.