It is not a mountain range in the normal sense, because it was formed as a single volcano that has been eroded for the past 5 million years.

It lies on the Chilcotin Plateau, located some 350 kilometres (220 mi) north-northwest of Vancouver and 30 km north of Anahim Lake.

They have lived in the area for hundreds of years, travelling when necessary to hunt and trap animals such as beaver, caribou, moose, and to gather plants and roots.

Like all glass and some other types of naturally occurring rocks, obsidian breaks with a characteristic conchoidal fracture, creating razorlike edges.

The Ilgachuz Range was created by two chemically separate magmatic periods; an early complex series of trachyte and rhyolite eruptions, and late extrusion of a sequence of basaltic lava flows.

The Precaldera Assemblage is best exposed on the east side of Pipe Organ Mountain where it contains a bedded pile over 300 m thick of weakly consolidated, moderately to extremely different, pyroclastics, flows and deposits of uncertain origin.

The northerly domes are subcircular talus mounds of plate sized pieces of light to dark grey, slightly porphyritic, flowbanded rhyolite with minor obsidian.

Similar material, grading up into finer debris flows and possibly lahars, has been uncertainly known in the gap between Phacelia Peak and Calliope Mountain suggesting this area is the southern edge of the caldera.

Alternatively, largely unsorted breccia and debris deposits exist on the ridge north of Saxifraga Peak, possibly indicating the main, or a subsidiary, caldera edge.

[1] The Shield Forming Assemblage contains a series of basalt and minor comendite eruptions, and is best exposed on Far Mountain and Mount Scot.