The ichnofossil Rusophycus is the product of a typical behavior of trilobites, but is only preserved under unique conditions. A unique confluence of conditions existed in the Middle Cambrian Gros Ventre environment and resulted in the preservation of a Rusophycus lagerstätte. These conditions include the background deposition of firm, cohesive muds possibly bound by bacterial mats. The muds had a firmness that allowed the burrows to maintain their shape until they were filled in and cast during the next phase of sand deposition, likely from a storm. The deposition of sands following episodic high energy events provided an ideal casting medium for Rusophycus. The absence of spreite and presence of individual storm events in sectioned Rusophycus support this conclusion. These results contradict previous assertions that the Rusophycus ichnofossil was excavated by trilobites burrowing through sand to a muddy interface. The Gros Ventre Formation falls in the middle of the Cambrian Substrate Revolution. Bacterial mats were present before, during, and after the deposition of the Gros Ventre Formation. Bioturbation indices for the Gros Ventre Formation are comparable to those documented for the Cambrian by other workers and support the idea of a gradual increase of bioturbation intensity during the Middle Cambrian.