The San Andreas Fault is a line which marks the border between two tectonic plates: The Pacific and the North American. It runs 800 miles through the length of California. Californians, especially Southern Californians, will talk of "The next big one", meaning the next big earthquake. This is because Central California had a big one in the 1850's, while San Francisco (in the North) had one in 1906, but Southern California is long overdue for a big earthquake, due to rising tension along the fault line.
The general worry is that, when this occurs, California will break off from the rest of the continent, looking somewhat like this:
This map was made in 1650, by a Dutch Cartographer named Joan Vinckeboons. Was he a brilliant geologist or a prescient cartographer?
It turns out he was neither. The San Andreas Fault, unlike most fault-lines, moves in a horizontal motion, not a vertical one. Therefore, while Los Angeles will probably move North of San Francisco at some point in the next 20 million years, a part of California will never break off to form an American Madagascar (Vinckeboons thought it already had). We should tell the Library of Congress they might as well throw this map away during their next spring cleaning session.