In 1997's "Volcano," Tommy Lee Jones and Anne Heche scramble as a huge volcano spontaneously appears from under Los Angeles, California spewing fireballs and lava that devastate the city.
Never mind that volcanos don't generally emerge abruptly and without warning. The movie would have you believe that these enormous geologic events can happen practically overnight.
The bigger issue is that there is no geological basis at all for volcanoes to occur in L.A. Volcanoes form only in subduction zones, that is, where one tectonic plate is slipping beneath another, subsequently unleashing hot magma that flows to the surface of the Earth's crust.
As it turns out, there is no subduction zone anywhere near California. The infamous San Andreas Fault is what's called a strike-slip fault. Here, the plates merely slide horizontally, rubbing against each other in way that doesn't allow for magma flow or volcano formation.
In cases where volcanos do from along strike-slip faults, they are typically smaller and less destructive. That means a horrifyingly huge magma monsters aren't going to upend West Coast cities anytime soon.