Analysis of emergent marine terraces in the San Joaquin Hills, California, and 230Th dating of solitary corals from the lowest terraces reveal that the San Joaquin Hills have risen at a rate of 0.21–0.27 m/k.y. during the past 122 k.y. Movement on a blind thrust fault in the southern Los Angeles basin has uplifted the San Joaquin Hills and has the potential to generate an Mw 7.3 earthquake within this densely populated area. Our structural modeling suggests that the fault dips to the southwest and slips at ∼0.42–0.79 m/k.y., yielding an estimated minimum average recurrence interval of ∼1650–3100 yr for moderate-sized earthquakes. Recognition of this blind thrust extends the known area of active blind thrusts and fault-related folding southward from Los Angeles into coastal Orange County.