Dotsero is a small volcanic complex in Colorado near the confluence of the Eagle and Colorado rivers, centered on an elongate maar called Dotsero Crater cut into Blowout Hill. Formed by a single eruption around 2220 B.C., it produced lava fountains, then explosive phreatomagmatic activity that excavated the maar and spread lapilli tuff, and finally violent Strombolian eruptions that built nearby scoria cones. Associated lava and lahar deposits reshaped the landscape, including diverting the Eagle River. Studied since the late nineteenth century, Dotsero is now recognized as one of Colorado’s few Holocene volcanoes and a scientifically important site with some potential for renewed activity.