peluvium is soil that has been deposited by gravity. san francisco, dune sand, colma, and the others. very simple. because san francisco is so young. -- because san francisco is so young, it is riddled by faults. i have a map that shows the faults across the bay area and san francisco. the granddaddy of all of these is the san andreas fault. it is the longest. it can generate the greatest earthquakes. >> it is just south of san francisco. it goes offshore down here. >> from my house to the fault is about 3 miles on average. >> the closest area in san francisco to the fault is this area here in the southwest part of the city. people said that the closer you are, there are conditions that exacerbate issues. >> the fault's effect on development depends on the fault type and soil component. the san andreas is the main fault. there is the hayward fault. the difference between the two is that the san andreas is predominantly offshore. the hayward fault actually crosses beneath populated areas and poses a larger threat. as we speak, there is a