The state of Washington is located in the northwesternmost corner of the U.S.A.. It is borderen by the Pacific Ocean to the west and Canada to the north. Most of the state os mountaineous, as the Rocky Mountains start right from the coast. As it is part of the belt of fire, there are numerous volcanoes in this area, the most well known is Mount St. Helens, which erupted really spectacular 20 years ago.
Many caves exist in Washington, most of them are lava tubes, produced by lava streams of the big volcanoes. This lava tubes are among the longest of continental U.S.A. and among the longest tubes of the World. They are only topped by the Hawai'ian lava tubes. Two of those caves are open for the public.
Although there are no big limestone areas, there are several small karst caves, located in small patches of limestone in volcanic material. Typical results of solution is speleogenesis in the contact between soluble and insoluble rocks. Rivers vanish when they reach the limestone in sinks and reappear in huge karst springs on the other side.
And there is a third category of caves which is common in Washington. Along the Pacific coast there are numerous sea caves, formed by the erosional force of the waves.