Timpanogos Cave National Monument, Limestone cave system in American Fork Canyon, Utah, US.

Timpanogos Cave National Monument protects three linked caves in the cliffs of American Fork Canyon: Hansen Cave, Middle Cave and Timpanogos Cave, joined by tunnels blasted in the 1930s. Inside are stalactites, stalagmites, flowstone, cave popcorn and twisted helictites, including the joined stalactite known as the Great Heart of Timpanogos. A 1.5-mile paved trail climbs 1,092 feet from the canyon floor to the entrance.

Martin Hansen found Hansen Cave in October 1887 while cutting timber, reportedly after tracking cougar prints up the canyon slope. In 1913 teenagers James Gough and Frank Johnson found Timpanogos Cave, but the entrance was lost until Vearl Manwill rediscovered it on August 14, 1921. That October the Hansen family found Middle Cave. The monument was designated on October 14, 1922, and the National Park Service took over in 1933.

The name Timpanogos comes from a Ute word for the Provo River, and the cave system takes its name from Mount Timpanogos above it. The monument's cultural life today centres on ranger-guided tours: groups of up to 20 enter through a man-made entrance near Martin Hansen's 1887 opening, pass into Middle Cave, then Timpanogos Cave, and leave by a man-made exit. The Great Heart of Timpanogos, a formation grown from several stalactites, is the feature visitors most often ask about.

The paved trail to the entrance is 1.5 miles long and climbs 1,092 feet, so allow time for the ascent. Tours are usually offered May through September, depending on snow and funding. Groups are capped at 20 people with at least 10 minutes between tours; in summer, reserve ahead because waits can last hours.

The cave's helictites are hollow, twisted, spiraling straws of calcite or aragonite that grow in directions unaffected by gravity. Water travels through the tube and evaporates, leaving a trace mineral deposit at the tip. Some are hollow enough for capillary effects to play a role; the growth of the thicker, more common ones is still not fully explained.