AN INVESTIGATION OF AMYGDALOIDAL BASALT IN THE CONEJO VOLCANICS FORMATION, SANTA MONICA MOUNTAINS, CALIFORNIA

Field mapping and mineralogical analysis were conducted on several layers of the Conejo Volcanics formation that are exposed in an outcrop in Triunfo Canyon, Agoura Hills, CA. The ~200 meter-long outcrop exposes moderately north-dipping volcanic stratigraphy. The bottom layer is amygdaloidal basalt, the vesicles of which are lined with palagonite, suggesting subaerial emplacement. The next layer is a (10m-thick) pyroclastic flow deposit capped by a layer of pillow basalt. The contact between the bottom two layers is a groundwater seep from which plants grow, suggesting that bedrock has a primary control on groundwater movement in the complex Conejo Volcanics formation.