The San Andreas fault is a big strike-slip fault. In a right-lateral fault, if you stand on one side and look at the other side, the other side moves toward your right. In a left-lateral fault, if you stand on one side and look at the other side, the other side moves toward your left. In this context, geology refers to looking at rocks, and in particular, noting rocks which are right next to each other and didn't form that way. Biology in this case means plants and where they grow.
Geophysics can mean lots of things, primarily earthquakes, magnetics, and gravity.
Not much else in nature makes straight lines. If you find a straight line that is natural, it's a good bet you're looking at a fault. You can use biology to find faults in certain situations, particularly in arid lands. Often, the rocks in a fault zone can become clayey, and act as a barrier to the flow of groundwater. When this happens, groundwater builds up on the uphill side of a fault, and the water table is raised relative to the other side of the fault.