English: Sometimes called the “smallest mountain range in the world,” the Sutter Buttes rise almost 610 meters (2,000 feet) above the flat agricultural fields of the Great Valley of central California. The Sutter Buttes are remnants of a volcano that was active approximately 1.6 to 1.4 million years ago during the Pleistocene Epoch. The central core of the Buttes is characterized by lava domes—piles of viscous lava that erupted onto the surface and were built higher with each successive layer. Today, these lava domes form the high central hills of the Buttes; shadows cast by the hills are visible at image center. Surrounding the core is an apron of fragmental material created by occasional eruptions of the lava domes. This apron extends roughly 18 kilometers east-to-west and 16 kilometers north-to-south (11 by 10 miles). The volcanic material was transported outwards from the central core by volcanic gas-driven pyroclastic flows or by cooler, water-driven lahars. Later stream erosion of the debris apron is evident from the drainage pattern surrounding the central core. A third geomorphic region of valleys, known as the “moat,” lies between the core and the debris apron, and was formed by erosion of older, exposed sedimentary rocks that underlie the volcanic rocks.