Strata of Jurassic age contain cylindrical bodies of sandstone called pipes. They cut gently dipping strata in the Summerville Formation, Bluff Sandstone, and Morrison Formation near Laguna, Now Mexico. The pipes range from a few feet to a few hundred feet in height, and from a few inches to 130 ft in width. Petrographic studies of the material in the pipes and of the enclosing strata show that the pipes are composed of reworked subarkosic sandstone derived from the uppermost units cut by the pipes. Some pipes are composed of brecciated sandstone and mudstone in a fine-grained matrix. The wall rocks sag downward around the pipes, and the pipes are bounded by one or more ring faults. The bottoms of the pipes are in sharp contact with the little-deformed underlying beds. The pipes formed during a period of gentle regional folding, and for the most part are located in belts near synclinal axes. Pipes originated during deposition of the uppermost sandstone units that contained them. They probably formed by gravitational foundering of sand into the underlying water-saturated mud. Some of the foundering may have been aided by solution and removal of underlying gypsum.