Final answer:
The San Andreas Fault is formed by the Pacific Plate and the North American Plate. Los Angeles is moving northward on the Pacific Plate. Over time, the distance between San Francisco and Los Angeles is changing due to the relative movements of these plates.
Step-by-step explanation:
The two tectonic plates that make up the San Andreas Fault are the Pacific Plate and the North American Plate. This fault is known as a transform boundary where both plates slide past each other. The Pacific Plate is moving northward relative to the North American Plate, which is largely stationary in comparison. As a result, the city of Los Angeles, located on the Pacific Plate, is also moving northwards over time. The San Andreas Fault runs from the Gulf of California to the Pacific Ocean northwest of San Francisco.
Regarding the question of the location of cities along the fault: Los Angeles is situated on the Pacific Plate, which is notorious for its seismic activity due to the movement of this tectonic plate. The sliding motion of these plates is responsible for the stress accumulation that can result in major earthquakes when the fault slips.
San Francisco and Los Angeles are slowly moving relative to each other; Los Angeles is inching closer towards San Francisco due to this northward movement. Over a sufficiently long timescale, it is hypothesized that Los Angeles may even become an island off the coast of San Francisco.