Mammatus formed in early of 2005, and played their first show at the Silent Planet in Corralitos on March 20, 2005. Since then they have played in living rooms and dive bars in Santa Cruz, opened for more reputable bands in San Francisco, and toured the United States three times and have gone to parts of Canada. With no money and no label Mammatus recorded four songs in their makeshift garage studio. The recording attracted the attention of Holy Mountain Records in San Francisco and The Rocket Record Company in the UK, who both released their self titled debut album on March 28, 2006. The artwork was done by the Arik Moonhawk Roper, who also provided covers for such bands as Sleep and High on Fire.
In the middle 2006 Mammatus returned from an American tour with label mates Residual Echoes. They returned to the studio and released "The Coast Explodes" in 2007.
Mammatus set on a North American tour in April and May 2007 with Acid Mothers Temple.