Bear River Lava

The sign's 28,000 years has not held up. Geologists now trace the Bear River's turn to lava from the Alexander shield volcano, near Soda Springs, and date the final diversion to about 55,000 years ago, when the blocked river spilled south over a low divide and cut Oneida Narrows. Earlier estimates ranged from 600,000 years to 35,000. The added river is a large part of why Lake Bonneville rose higher than any lake before it, and the Bear still supplies about a third of the fresh water reaching Great Salt Lake.

What the plaque says

Bear River Lava Until about 28,000 years ago, Bear River used to flow northwest from here through Portneuf Canyon into Snake River. Then these lava eruptions blocked that route, diverting Bear River south into what now is Salt Lake. At that time a large inland sea--known as Lake Bonneville--covered much of Utah. Additional water from Bear River helped make it overflow into Snake River before a change in climate dried it up about 8,000 years ago. 220 Text prepared by the Idaho Historical Society Marker made & installed by Idaho Transportation Department

Where it stands

Worth the stop nearby

• Soda Springs Geyser — 5.0 mi
  Drillers looking for hot water for a swimming pool hit cold soda water under pressure. The town put the geyser on a timer.
• Black Canyon of the Bear River — 5.5 mi
  A basalt gorge cut by a river that, most of the year, now runs past it in a pipe.
• Lava Hot Springs — 16 mi
  The pools belong to the state because the springs left the Fort Hall Reservation and Congress handed them to Idaho in 1902.
• National Oregon/California Trail Center — 31 mi
  Emigrants came down off Big Hill and camped in the clover here. Brigham Young renamed the town; the trail center brings the camp back in costume.

More markers nearby

• John Bidwell — steps away
• Soda Springs — 3.9 mi
• Camp Connor — 3.9 mi
• Hooper Spring — 5.1 mi