The first quarter of the 19th century showed the continuation of the slow colonization of the southern and central California coast by Spanish missionaries, ranchers and troops. By 1820 Spanish influence was marked by the chain of missions reaching from Loreto, north to San Diego, to just north of today's San Francisco Bay Area, and extended inland approximately from the missions. Outside of this zone, perhaps 200,000 to 250,000 Native Americans were continuing to lead traditional lives. The Adams–Onís Treaty, signed in 1819, set the northern boundary of the Spanish claims at the 42nd parallel, effectively creating today's northern boundary between California and Oregon.