Oligocene to Miocene sandstones of the Temblor Formation in the west central San Joaquin basin consist of poorly sorted to well sorted arkosic to lithic arenites deposited in environments ranging from fluvial to deep-basin turbidity flow, but most of the sands were deposited in marine shelf environments. Primary porosity was rapidly destroyed due to a combination of burial and tectonic compaction; compaction also resulted in fracturing of brittle grains and deformation of labile components. Deformation of labile grains, especially volcanic rock fragments, resulted in formation of pseudomatrix that was squeezed into adjacent pore spaces drastically reducing porosity. In arenites containing few labiles compaction caused fracturing of brittle grains; this in turn exposed unweathered material to diagenetic fluids resulting in widespread dissolution and creation of secondary porosity. Continued compaction caused both primary and secondary pores to collapse, resulting in sands whose textures and mineralogy have been altered and in which secondary porosity has come to resemble primary porosity. With deep burial, continued compaction further reduced porosity to very low levels unless through-going fractures were forming to act as conduits for diagenetic fluids. Data indicate that feldspathic arenites may retain significant porosity to depths in excess of 20,000 ft but lithic arenites are unlikely to retain significant porosity below 10,000 ft. Thus, target rock mineralogy should be an important consideration when designing exploration programs for deeply buried hydrocarbons in the San Joaquin basin.