Adobe was the principal construction material used in the arid north of Mexico. In wetter parts the adobe was subject to water damage: rain ate away its exposed surfaces and softened the ground on which the terrifically heavy bricks rested. Keeping an adobe intact would have meant keeping the walls limed and the roof watertight. Ideally, it would also be built on a stable site with good drainage, which was perhaps not always possible.
The adobe in Wilder Ranch State Park (CA-SCR-123/38) was found by Kent Lightfoot to have been built on top of a shellmound. A lot has changed around it in the interim and the house is not now perceptibly higher than its surroundings.
Was building on the shellmound a deliberate plan to support structural stability? Were other coastal adobes built in such places too?