Earth movement is excluded across the board
Earthquake, landslide, subsidence, settling and sinking are excluded on standard homeowners forms, and the exclusion generally applies regardless of what caused the movement. It is one of the broadest exclusions in the contract and one of the least discussed, because nothing about a desert suburb suggests it matters.
Settling cracks are not an insurance problem
Hairline cracking in stucco and drywall as a house settles is normal and uninsured. What matters is distinguishing ordinary settling from movement serious enough to need engineering, and that is a structural question rather than a claims one.
Separate cover exists and it is a real decision
Earthquake and earth movement cover can be bought separately in some circumstances, usually with a substantial percentage deductible. Whether it is worth it depends on the house and your tolerance, and it should be a decision rather than an omission.