The Salten Sea was created by flooding with ocean water. Dig a trench around San Francisco, below sea level. Flood the area.
Add boat docks.
Over millions of years, the Colorado River has flowed into the Imperial Valley and deposited soil (creating fertile farmland), building up the terrain and constantly changing the course of the river.
For thousands of years, the river has alternately flowed into and out of the valley, alternately creating a freshwater lake, an increasingly saline lake, and a dry desert basin, depending on river flows and the balance between inflow and evaporative loss.
The cycle of filling has been about every 400–500 years and has repeated many times. The latest natural cycle occurred around 1600–1700 as remembered by Native Americans who talked with the first European settlers. Fish traps still exist at many locations, and the Native Americans evidently moved the traps depending upon the cycle.
The most recent inflow of water from the now heavily controlled Colorado River was accidentally created by the engineers of the California Development Company in 1905. In an effort to increase water flow into the area for farming, irrigation canals were dug from the Colorado River into the valley. The canals suffered silt buildup, so a cut was made in the bank of the Colorado River to further increase the water flow.
The resulting outflow overwhelmed the engineered canal, and the river flowed into the Salton Basin for two years, filling the historic dry lake bed and creating the modern sea, before repairs were completed.[2]