How was the northern border of California set?

A good number of visitors to Fort Vancouver seem to wonder why it flew the British flag (inside the HBC flag). That often brings mention of the the Treaty of Joint Occupancy of October 1818, including the usual phrase, “from the ridge of the Rockies to the Pacific, and from California to Alaska.” If the visitors are from California one of my favorite questions is to ask them if they know when the northern border of California was set, and how. So far I have not had a correct response. It seems to be one of those questions that isn’t a question until it is asked. The answer, it turns out, has more to do with Seminole raids from Florida into Georgia than it does with surveying a line across the Siskiyou Mountains. The quick version:

            In March 1818 Andrew Jackson took it upon himself to invade northern Florida in what is called the first Seminole war. At the time Florida was under Spanish possession, but hardly control. Spain was exhausted from a destructive decade of the Napoleonic wars, during which most of its American colonies had declared independence. There were few Spaniards living in Florida and it was more trouble than it was worth to Spain, which was ready to trim its losses and give it to the USA. “But wait,” the Spaniards in effect said to the Americans, “While we’re putting those useless swamps and troublesome Seminoles in your hands, let’s settle the poorly defined border between the Louisiana territory you bought from France in 1803, and our Mexican colony to the west.” US Secretary of State John Quincy Adams and Spanish Foreign Minister Luis de Onís began trading proposals, resulting in the Adams-Onís treaty of February 1819 which established the border shown in the red line in this map:

 The treaty set the northern border of what became the states of Utah, Nevada, and California at the 42^nd parallel of north latitude. That line was more than 300 miles north of Sonoma, Spain’s northernmost settlement in California, which probably seemed to the Spaniards like plenty of buffer zone.

            Before the 1819 treaty Spain still claimed rights in principle over the entire west coast of North America, based on a papal grant dating from 1493. They had tried to make good on that claim as far north as Nootka Sound on Vancouver Island in 1789-90, but the intruding British managed to chase them off, and they pulled back to central California. By the Adams-Onís Treaty the king of Spain gave the United States, “all his rights, claims, and pretensions to any Territories, East and North of the said Line, and . . . renounces all claim to the said Territories forever.” That was the first basis in international law for a claim by the United States to a piece of the coastline of the Pacific Ocean and the adjacent mainland--Lewis and Clark in 1805 and the Astorians in 1811 had no prior legal basis for being west of the Rockies.  So the treaty with Spain that fixed the California border also provided a legal precedent for eventual US claims in its dispute with Great Britain over Oregon Country/Columbia District, finally settled in the Oregon Treaty of 1846.

            Here’s an interesting tidbit: The first Spanish proposal in the back-and-forth had a line extending from the ridge of the Rockies along the 41^st parallel to the headwaters of the Willamette River, then following the Willamette north to its mouth (present site of Portland), and from there down the Columbia to the Pacific.* If that proposal had been accepted and then held, and if the British had later managed to make the Columbia river the southern border of their Canadian colony, then the people in West Portland (and everyone on the west side of the Willamette River) would be speaking Spanish, people in East and North Portland would fly the Stars & Stripes and celebrate the 4^th of July, and the population of Vancouver, WA and Seattle would be saying "aboot" and welcoming William and Kate as the future king and queen of their country. The USA would have had no territory bordering anywhere on the Pacific Ocean. But that didn’t happen.

* William E. Weeks, John Quincy Adams and American Global Empire (Lexington: University of Kentucky Press, 1992), p. 161.