Mount Hood is an active volcano and a center of seismic activity. Earthquake clusters occur annually. July 1980 and June 2002 very significant movement near Mount Hood was confirmed at the USGS Cascades Volcano Observatory in Vancouver, Washington. The most recent major eruption at Mount Hood occurred in 1781–82 with smaller eruption occurring in 1805 just before the arrival of Lewis and Clark.
While motorist probably don’t need to worry about a Mount Hood eruption, seismic activity along with natural erosion very significantly increases the probability of injury accident due to slide or falling rock. In 2006, Mt. Hood Meadows could not open as scheduled due massive debris slides at the White River and Newton-Clark brides. Mount Hood Meadows was isolated for six weeks due to highways destroyed and blocked these flows. Removing debris cost about $5M.
Problems at OR 35 and the White River are not new. Before 1950 this intersection was regularly overwhelmed by upstream discharges of water, tree and boulders. Finally, in the 1950s the OR 35 Bridge at White River was raised nine feet to increase clearance. The 2006 event confirmed that nine feet was not high enough. As a result, a new $40 million project scheduled for the bridge over the White River to be raised 10 to 12 feet with an extended span. You now can see the frame of new bridge at the site.