This part of Mexico is in a complex tectonic regimen. Starting 14 million years ago, extension across the present-day Gulf of California commenced. Extension further occurred during the Pleistocene in the adjacent Mexican mainland in the Tepic-Zacoalco rift, which separates the Jalisco block from the Sierra Madre Occidental, and the Colima rift zone with its probable submarine extension, the Manzanillo canyon. Volcanism and earthquake activity is still ongoing in these rift zones today, forming for example Ceboruco and Volcan Colima which is Mexico's most active volcano. These two rift zones together with the Middle America Trench delimit the Jalisco block.