San Pedro, Stratovolcano in El Loa Province, Chile

San Pedro is a stratovolcano in Chile's El Loa Province, located in the high Andes and made up of two cones that formed at different times. The two structures sit one over the other, giving the mountain a double-peaked outline that stands out clearly across the surrounding plateau.

The Old Cone was active more than 100,000 years ago until a giant landslide removed its northwestern side, leaving a scar 120 square kilometres in extent whose front stands 35–40 metres high in the Pampa de la Avestruz. Within that scar, lava and pyroclastic flows built the Young Cone and the lateral centre La Poruña. A Plinian eruption at the start of the Holocene left the El Encanto ignimbrite, and eruptions were reported into historical time; the last was in 1960.

San Pedro's name is shared with the San Pedro River below and the railway station southwest of the cone; sulfur was mined on the summit into the 1930s, and tracks left by those miners still lead up the mountain. Chile Route 21 runs around its northern and western flanks.

Old trails left by former sulfur miners point toward the summit and can help climbers find their way up the mountain. The road that passes along the northern and western sides does not go to the top, so coming prepared with a clear route plan is important.

The younger cone produced different types of lava during separate eruptions, including andesite and dacite, which stacked in visible layers. This pattern of alternating materials makes the internal structure of the volcano of particular interest to geologists.