In May of 1981, a reconnaissance trip to the Santo Domingo Canyon looked at Cueva de la Peña Colorada, an enormous fossil resurgence cave. Later in 1982 Sump 1 was explored for 524 meters to where it opened into an air-filled tunnel. A further kilometre of dry cave leading northward towards Sistema Huautla was then discovered. Sadly, exploration was halted by the discovery of a second sump. Connecting this tunnel with the deepest known point in Sistema Huautla (10 kilometers away and 300 meters higher) became the primary objective of the 1984 expedition.

A total of 7.8 kilometers of virgin territory leading into the plateau were surveyed on this expedition, with 1.4 kilometers of this distance totally underwater. This was comprising of 7 sumps, the longest of which was 524 meters in length. The expedition established the first ever subterranean camp set beyond an underwater tunnel. 

The team was stopped by sump 7 - a large sump at the bottom of a 55 meter deep shaft (with no dry land). This was explored for 165 meters to a depth of 55 meters. This has now been more than three decades ago, and nobody has returned since.

Further reading:

  • Stone, B., 1984, The Challenge of the Pena Colorada. AMCS Activities Newsletter 14:46-55. [pdf]