Saguache County has the remains of several volcano's. The Bonanza Caldera can be seen as you drive north of Monte Vista on US Highway 285. 12,129 Hayden Peak can be seen to the right of 285 and 13,268 Antora Peak to the left. These two mountains mark the east and west edges of the Bonanza Caldera which in nearly eight miles across. The town of Bonanza lies near the center of the caldera.
 
The very center of the Summer Coon lies in Saguache county. It created lava dikes with probably one of the last eruptions. These dikes appear much the same as spokes of a wagon wheel. Hell's gate and La Ventana (or window) are part of one of these dikes. The La Garita Volcano first erupted about thirty-five million years ago and is reported to have been twenty thousand times more powerful than Mount Saint Helens. The boundaries of the volcano extends from Wolf Creek Pass, southwest of Monte Vista, fifty miles to the north and is the remains of the largest volcano on earth.
 

The San Juan Mountains to the west of the San Luis Valley are made up of several volcano's. the Summer Coon and the Platoro are a couple of these. The Summer Coon and the Platoro volcano's form most of the mountains which we see from the center of the valley. Others volcano's are present deeper into the San Juan mountains. The Bonanza volcano created the mountains at the north end of the valley.
 
The Sangre de Cristo Mountains to the east are the earths crust which has pushed up by over riding the earths crust to the west of the fault line. They began forming about twenty-eight million years ago. There is some much older volcanic activity in places along the mountain range. Mines have been located on about every stream running from the mountains.