Oregon caves

Valley leading up to Oregon Caves
National Monument.

The Oregon Caves National Monument lies in the Siskiyou range, a mountainous region in southwest Oregon rich in biodiversity.

Dozens of chambers and tunnels connect the caves in a complex underground maze discovered by Elijah Davidson in 1874 while in pursuit of his dog and a bear that had entered the cave. The caves became a popular attraction; today the National Park Service leads tours of a little over an hour through much of the cave complex.

"Drapery" formed by sheet flow of water though
the cave.

The caves formed over the course of thousands of years as weak carbonic acid slowly dissolved the marble rocks underlying the mountain. The acids formed from the interaction of water with carbon dioxide released from decaying plant matter in the soils overlying the bedrock. The caverns and tunnels vary in size and shape. A very small stream (named the “River Styx”) runs through a part of the cave complex.

Slow mineral deposition over time as water continues to move through the caves has resulted in a variety of interesting forms inside many of the rooms. Dripping water creates forms such as stalagmites and the thin “soda straws” that project from some of the cave ceilings. Flowing sheets of water over rock surfaces form other shapes such as “drapery”. Lights set up by the Park Service help illuminate many of the features for visitors. 

Other cave features: stalagmites, stalactites, and
columns (fused stalagmites + stalagtites).

Drapery is most ornate in the "Paradise Lost" room,
my favorite place along the tour route.

Other reference

National Park Service educational materials