Above the Topanga Formation, a volcanic unit of lava flows and volcanic mudflows accumulated. This rock unit is called the Conejo Volcanics and has been dated at about 17,000,000 years old. This unit is the same age and has the same origin as the lava flow rocks called the Middle Topanga Formation that were seen in Griffith Park. Shown here is a lava flow unit of basaltic composition that consists of broken fragments of lava pillows mixed with lava that has since cooled into rock. Lava pillows are created when lava is extruded from an underwater flow in the shape of blobs, or pillows. These fine-grained, pillow-shaped, obsidian-like blobs cool quickly, shatter in the cold water, break up into smaller pieces, and then become engulfed in the advancing lava flow.