I currently have a 1950's home in the San Francisco Bay Area (Antioch to be exact). Around the doorways, windows, and in other erroneous spots there are cracks in the drywall. Some are severe while others are hairline. I have repaired them, to only have them re-appear a few months later. My house sits at the bottom of a small hill and is supported by huge rock retaining walls. Some people have told me that this is a result of the ground shifting, while others have recommended the services of a structural engineer as no house should have these issues - please help!