Many of our visitors have wondered if the elongated columns of rock that are observed in various parts of our Park are petrified logs, i.e. logs that were neatly arranged in piles and bundles, then turned to rock by some unknown and uncanny process. It is found in our lava flows and dikes, and is due to the regular development of prismatic joints that break up the rock mass into parallel columns, the sides of which are characteristically five or six in number. This rock phenomenon is known as columnar structure. While most of the columns will portray a rough and irregular hexagonal outline, many of them will have the sixth side so depressed and small that it is entirely eliminated.

This structure is variously portrayed in our Park. It may be observed at the following localities within the Rim Area: (1) the upper exposed portions of the andesite dike about two hundred yards west of the foot of the Lake Trail; (2) in a small area some forty feet above the Lake and fifty yards west of the dike just mentioned; (3) the Devil's Woodpile some seven hundred yards west of the foot of the Lake Trail (this feature is observed on the lake excursions under the guidance of some member of our Naturalist Staff); (4) parts of the dike known as the Devils' Backbone; (5) near the base of the great dacite flow that forms Llao Rock; (6) the constriction at the base of the bowl portion of the Wineglass; and (7) in the lava flow on the inside of the Rim below Kerr Notch. Near the crest of the steep portion of the grade over Vidae Ridge, and facing Sun Creek Valley some six-tenths of a mile southwest of the Sun Creek crossing another exposure of columnar lava may be observed. Here the lava has been poured onto a trifaceous agglomerate (a chaotic assemblage of coarse volcanic ashes and cinders). The attitude of the lava readily suggests its direct relations to the former mountain.