Dendrite Butte Limb Cast Site

At Dendrite Butte the stone to look for is shaped like a branch. Limb casts formed where hot volcanic ash buried pieces of wood and burned them out completely, leaving molds. Later, agate filled each cavity in the shape of the original limb. Many specimens show bark, knots, and wood grain on the surface. The Ochoco National Forest says casts with a green or pink hue are highly prized.

The butte lies southeast of Prineville in Crook County. It is one of several public rock-collecting sites there managed through the Bureau of Land Management. The Forest Service lists it with nearby Congleton Hollow as a single area under the name Paulina, the only limb-cast site on its list, and names both the BLM and the Ochoco National Forest as managers. Collecting is free. In 2020 The Bulletin noted that many of these areas are surrounded by private property, which must be respected at all times.

The rules are short. Ochoco geologist Carrie Gordon told The Bulletin in 2008 that rockhounds at Dendrite Butte, Congleton Hollow, and Maury Mountain may dig with shovels and take home what they find. They may not use mechanized digging equipment or blast through the rock. “The thing is (taking) reasonable amounts — what we’re talking about is personal collecting,” she said. “This is not for the commercial operator that wants to work the product and sell it.”

The sources give different limits. The 2020 Bulletin article set the limit at 25 pounds a day plus one piece, with no more than 250 pounds a year. A BLM collecting guide for Oregon and Washington applies that figure to petrified wood. For other rock, the guide describes a reasonable daily amount as one that fits in a car trunk or makes a partial pickup load and weighs under 250 pounds. Collecting vertebrate fossils or historical artifacts is prohibited.

These sites first went onto a map in the 1960s, when local chambers of commerce maintained some of them. Four years before The Bulletin’s 2008 story, the Forest Service, the BLM, and the Prineville-Crook County Chamber of Commerce updated the map. They added Global Positioning System coordinates, a briefing on local geology, and a rockhound’s code of ethics. The chamber and Wagner’s Market sell it for $10.