This prickly pear on Lasky Mesa appears to have many of the characteristics of the Engelmann prickly-pear, Opuntia engelmannii, but is more likely a cross involving O. engelmannii. One such cross is O. littoralis X (O. engelmannii X O. phaeacantha ) which is referred to as O. ×occidentalis in the Jepson Manual. Here's a closer view of the stamens and pistil.

From a run in in Upper Las Virgenes Canyon Open Space Preserve (formerly Ahmanson Ranch) on May 23, 2007.