24 1987 McClellan Mountain in the Los Angeles area has an interesting geological history. It was formed from volcanic activity during the Miocene epoch, about 15 million years ago. The mountain is composed mainly of andesite and rhyolite, which are types of igneous rock. The name "McClellan Mountain" comes from General William Tecumseh McClellan, who led Union forces during the Civil War. He was known for his cautious approach to battle, which sometimes caused him to be criticized by his superiors. Today, McClellan Mountain is a popular hiking destination for locals and tourists alike. Its trails offer beautiful views of the surrounding landscape, including the San Gabriel Mountains and the Los Angeles Basin.