Abstract The best-exposed natural bedrock outcrops in Michigan's southern peninsula are Upper Carboniferous (Pennsylvanian) sandstone ledges underlain by silts, clays, and coals in classic midcontinent ‘cyclothem’ stratigraphy, exposed along the Grand River in the city of Grand Ledge. Native Americans used the underclay in pottery; later commercial mining was the basis for clay-products factories. In the 1800s, the ledges provided a picturesque setting for a resort economy. Among the beneficiaries of repurposed quarries (now parks) are generations of Michigan geoscience students. A trip to Grand Ledge is often the first geology field experience for many students and plays an important role in the professional development of practising geoscientists and geoscience educators in Michigan. After an announcement of plans to expand the city's water treatment plant, adjacent to the cyclothem exposure, geologists from academia, government, and industry united to support preservation of the outcrops. City officials, previously unaware of the geoheritage value of the rocks exposed in their parks, are willing to work with geoscientists to preserve the site. This experience underscored the importance of documenting the geoheritage of the Grand Ledge area and establishing relationships with those who have oversight of these ‘greatest outcrops’ to ensure their preservation for future generations.

Abstract The Middle Cambrian Gros Ventre Formation (north-central Wyoming, USA) contains a lagerstätte of Rusophycus (arthropod ichnofossils) preserved in convex hyporelief on the base of sandstone beds or as sand lenses within beds of silty mudstone. Rusophycus was produced by typical trilobite behavior but was preserved only under the particular confluence of conditions that were common during the deposition of the Gros Ventre Formation. These conditions include the background deposition of firm, cohesive muds bound by bacterial mats, which allowed the burrows to maintain their shape until cast by episodic sand deposition. The absence of spreiten and presence of storm event bedding within sectioned Rusophycus specimens support this scenario and contradict previous assertions that Rusophycus was formed within the substrate. Chondrites were also present, extending its range into the Middle Cambrian. Bacterial mats and microbially induced sedimentary structures were present before, during, and after the deposition of the Gros Ventre Formation. Bioturbation indices are comparable to other Middle Cambrian sites, supporting a gradual increase of bioturbation intensity during the Agronomic and Cambrian Substrate Revolutions.