Those basalt columns on the Rivers of America are along the section the Disney Parks Blog referred to as the "Columbia River Gorge" section. And I remember commenting in this thread that it was a mistake to try and recreate something on that huge scale at Disneyland.
The Columbia River Gorge has lots of basalt columns on display, due to the widespread volcanic activity that formed nearly that entire region millions of years ago. Here's Beacon Rock just east of Portland, where Lewis & Clark camped for a time on their epic discovery of the Pacific Northwest.
Those are basalt columns. But they tower a few hundred feet high above the river, unlike the versions at Disneyland which are only a couple feet tall. Again, I have to question the attempt at recreating something as huge as the Columbia River Gorge at Disneyland.
On the other hand, Walt did recreate the Grand Canyon for Disneyland too.
EDIT: Here's some smaller basalt columns on the Columbia, but several hundred miles east out in Eastern Oregon where the Columbia River cuts through the very dry high dessert east of the Cascades.