Much of eastern Washington is underline by the Columbia River Basalt Group. The eruptions took place primarily in northeast Oregon between 17 and 14 million years ago. In central Washington the large lava flows encountered rivers flowing from the north and possible the west. The flows would have dammed the rivers forming lakes. Subsequent lava flows flowed into those lakes. The Columbia River's subsequent carving a deep valley into the basalt flows with some enhancement with the large ice age floods provides exposures to the lava/lake interactions. The interaction of lava flows with water and lake sediments can readily be seen along numerous road cuts and outcrops (columns-and-palagonite) including Interstate 90 west of Vantage. A basalt flow invading lake sediments like an intrusion can be seen at the top of McNeil Canyon north of Chelan (invasive-basalt-at-top-of-mcneil-canyon).
Along Highway 28 south of Wenatchee there are great exposures of multiple large lava flows. South of Moses Coulee there is a palagonite rich layer that shows foreset bedding structure.
Angled units within the yellow palagonite and basalt. Younger lava flows on the cliff top did not interact with water and developed columnar joints upon cooling.