A large and exceptionally well-preserved collection of dinosaur swim tracks, attributable to the ichnogenus Characichnos, is preserved as natural casts and reported in detail for the first time from the St. George Dinosaur Discovery Site at Johnson Farm (SGDS) in southwestern Utah. Approximately 3200 individual claw marks, typically in sets of three and rarely singular or paired, were made predominantly by small theropod dinosaurs in a size range consistent with the ichnogenus Grallator. About 95% of all dinosaur footprints on multiple track-bearing horizons at the SGDS are Grallator ichnites. Larger and less abundant Eubrontes-type swim tracks are associated with Grallator-type swim tracks at the SGDS.“Typical” Eubrontes and Grallator footprints occasionally occur among the swim tracks, providing further support for referring to swim tracks as “Eubrontes-type” and “Grallator-type.” Abundant invertebrate grazing traces and burrows indicate organic-rich, well-oxygenated sediments within the upper 1-2 cm of mudstone directly below the infilling sandstone unit of the SGDS “Main Track Layer” in which the swim tracks are preserved. Well-preserved sedimentary structures associated with a marginal lacustrine shoreline paleoenvironment suggest multiple animals swimming and/or floundering, mostly in a southerly direction, against a north-flowing current that paralleled the paleo-shoreline. Simultaneous formation of swim tracks on a clay-rich substrate, together with rapid burial of the traces, has resulted in exceptional preservation of skin impressions, scale scratch lines, and possible fine details on the cuticle of claw tips.