 Outside of this zone, perhaps 200,000 to 250,000 Native Americans continued to lead traditional lives.The Adams-Onís Treaty, signed in 1819 between Spain and the young United States, set the northern boundary of the Spanish claims at the 42nd parallel, effectively creating today's northern boundary of northern California.Russians, from Alaska, were moving down the coast, and in 1812 established Fort Ross, a fur trading outpost on the coast of today's Sonoma County.