Who built the spanish missions in california?

The missions were built by the Spanish starting in 1769 in order to "colonize" the territory of Alta California, which they had discovered over two centuries earlier. There had been various proposals over the years to do something with this territory, but it was hard reaching the coast of Alta California from New Spain (Mexico) in those days, sailing against the wind and currents, and Spain had other priorities. What finally moved them to act was the fact that Russian fur trappers were moving farther and farther down the Coast (from their bases in Alaska) and were spotted near present day San Francisco in 1760s.