Challis Arc

The Challis Arc was an Eocene volcanic field that stretched from southwestern British Columbia through Washington to Idaho, United States.

[2] Remnants of the Challis Arc are found as granitic plutons in the North Cascades, the Okanagan Highlands and in southcentral Idaho.

It was first theorized in 1979 that the volcanic field formed as a result of subduction of the eastern block of the Kula Plate between 57 and 37 million years ago.

Another model suggests that intracontinental rifting and igneous activity between the Pacific and North American plates formed the Challis arc.

[2] The current limited availability of historical geochemical data prevents any of the proposed theories from being confirmed or falsified, so there is still no consensus on the Challis Arc's formation.