This colour satellite image shows part of the San Andreas Fault in California, on the west coast of the United States. The fault, which represents the boundary between the Pacific and North American tectonic plates, is clearly visible as a line running southeast to northwest across the picture. To the north above the fault, brown indicates arid, grassy plains, while to the south green areas indicate wetter, forested mountains, different because of the distinct geological and climatic conditions encountered either side of the fault. A second fault, the Garlock Fault, meets the San Andreas Fault left of center, and shows the same landscape contrast to either side.