Meniscate burrows from Miocene lacustrine-fluvial deposits, Diligencia Formation, Orocopia Mountains, Southern California

About 20 specimens of ?Muensteria ichnosp. burrows were found at one locality in the lower Miocene Diligencia Formation of Southern California. The burrows are cylindrical, unlined and internally meniscate, up to 20 cm in length and 2 cm in diameter, and mostly horizontal. Some have vertical to oblique passageways where they pass from one bedding plane to another. Burrow morphology most closely resembles Muensteria von Sternberg, 1833. This heterogeneous ichnogenus is in need of taxonomic revision and most likely is synonymous with various other stuffed burrows (i.e., Taenidium, Laminites, Scoyenia, etc.). The meniscate structures indicate that infaunal deposit-feeders, possibly aquatic oligochaetes, backfilled their burrows in deposits where a braided river entered a lake.--Modified journal abstract.