Fresno is a good place to build underground dwellings for several reasons:

1. not much rain, little chance of flooding
2. lots of ag/city interfaces for actually being able to see the ground surface

3. and most importantly, most of Fresno is built on an old (~ 150,000 years) and stable alluvial deposit which has a subsurface feature known as a duripan a silica cemented horizon ranging from several inches to several feet thick. The subsoil is dry and loose, which helps digging out a home once you penetrate the duripan. It is likely that he built his home under the San Joaquin soil series, know for its well developed duripan (and the CA state soil!).

-- A Fresno Native and soil scientist --