About 30 miles southwest of Grants Pass  is the Oregon Caves National Monument (Rte. 46, 541/592-3400, www.nps.gov/orca , $8.50 adults, $6 children ages 6–11). The cave itself—as there is really only one, which opens onto successive caverns—was formed over the eons by the action of water.
As rain and snowmelt seeped through cracks and fissures in the rock above the cave and percolated down into the underlying limestone, huge sections of the limestone became saturated and collapsed—much as a sand castle too close to the sea always caves in. When the water table eventually fell, these pockets were drained, and the process of cave decoration began.
First, the limestone was dissolved by the water and carried in solution into the cave. When the water evaporated, it left behind a microscopic layer of calcite. This process was repeated countless times, gradually creating the beautiful formations visible today.
When the minerals are deposited on the ceiling, a stalactite begins to form. Limestone-laden water that evaporates on the floor might leave behind a stalagmite. When a stalactite and a stalagmite meet, they become a column.
Other cave sculptures you’ll see include helicites, hell-bent formations that twist and turn in crazy directions; draperies, looking just like their household namesakes but cast in stone instead of cloth; and soda straws, stalactites that are hollow in the center like a straw, carrying mineral-rich drops of moisture to their tips.
Discovered in 1874, the Oregon Caves attract thousands of visitors annually. During the Depression, walkways and turnoffs were built to make the cave more accessible. Unfortunately, tons of waste rock and rubble were stashed in nooks and crannies in the cave instead of being transported out. This had the ironic effect of obscuring the very formations meant for display. However, the National Park Service started to remove the artificial debris in 1985, exposing the natural formations once again. Little by little, the cave is returning to the way it looked before the “improvements” began.
The River Styx, another victim of Depression-era meddling, is enjoying a similar resurrection. This stream used to run through the cave but was diverted into pipes to aid trail and tunnel construction. The pipes ended up buried beneath tons of pulverized rock, and now the Park Service is hard at work undoing the work of humans to let the stream flow where nature intended.
Tours of Oregon Caves are conducted year-round by National Park Service interpreters. Their presentations are both informative and entertaining, and you will leave the cave with a better understanding of its natural, geological, and human history. A recent discovery in an unexplored part of the caverns was a grizzly bear fossil believed to be over 40,000 years old.
Children younger than age 6 must pass ability requirements (e.g., walking up many stairs for a total vertical climb of 218 feet) and stand a minimum of 42 inches tall to gain entry. The tour, limited to 16 people, takes a little over an hour and requires some uphill walking.
Good walking shoes and warm clothing are recommended. It may be warm and toasty outside, but the cave maintains a fairly consistent year-round temperature of 41°F. Passageways can be narrow, ceilings low, and the footing slippery. During summer you can wait in line up to an hour to go on a tour, and fewer tours are offered October–April. Call ahead for tour times.
To get to Oregon Caves National Monument, take U.S. 199 from Grants Pass  to Cave Junction, then wind your way 20 miles up Route 46 (a beautiful old-growth Douglas fir forest lining the road might help distract the faint of heart from the nail-biting turns). The last 13 miles of this trip are especially exciting. Remember that there are few turnouts of sufficient size to enable a large vehicle to reverse direction.