British Columbia and Montana will work together to protect a tiny piece of the province described as a missing piece of a world heritage site.

A deal to be signed Thursday between Premier Gordon Campbell and Gov. Brian Schweitzer sustains environmental values in the Flathead River Basin, an area in the extreme southeastern corner of B.C., bordered by Glacier National Park in Montana.

The pact is being called "conservation gold" by the Sierra Club of B.C., in part because Campbell has agreed to ban mining, oil and gas development in the region.

But environment groups said there's still a need to create a national park in the lower third of the valley and a wildlife management area through the rest of the valley and its adjoining habitat.

"B.C.'s Flathead River Valley is so exceptional that it needs the permanent protection offered by a national park in the lower one-third of the valley, adjacent to Waterton-Glacier International Peace Park," said Chloe O'Loughlin, executive director of the Canadian Parks and Wilderness Society."

Sierra Club spokeswoman Sarah Cox said the agreement recognizes that nature has no national boundaries and that B.C. and Montana must work together to protect shared fish, wildlife and water.

The Flathead Valley extends south into Montana and the B.C. region is considered the missing piece of the Waterton-Glacier International Peace Park.