The river crosses the international boundary at 49°00′00″N 120°19′37″W / 49.00000°N 120.32694°W / 49.00000; -120.32694 and transits Cathedral Provincial Park.

It has one main tributary, Ewart Creek, which is about 25 kilometres (16 mi) long and begins virtually at the border and is entirely within Cathedral Park.

The locality of Ashnola was that of a mining camp from the days of the many gold rushes in the Similkameen Country and also the site of the Ashnola Indian Reserve (attached to the Lower Similkameen Indian Band).

[1] Older name-variants includes Nais-nu-loh and Ashtnolow (both from Lord, 1860), Ashtnoulou (1861), Ashnoulou River, Trutch, 1871.

British Columbia Place Names, a semi-authoritative work on the toponymy of British Columbia, says the original form of the name is that of the Indian village formerly at the Ashnola Indian Reserve, which in the modern spelling system of the Okanagan language is rendered Acnulox.