The bedrock for much of Washington and Oregon, east of the Cascades, is basalt–the remains of lava that spewed into vast sheets covering more than 80,000 square miles. The vast bulk of the flows occurred between 14 and 17 million years. When the lava comes into contact water it often changes shape and color and hardens into a sharp, glass-like material known as palagonite that occasionally includes volcanic glass. The Deep Creek gorge west of Spokane has some of the most colorful palagonite, in Grande Ronde basalt deposited nearly more than 16 million years ago.