The teeth of many large herbivores contain “pockets” (fossettes, fossettids, etc.) which entrap impacted samples of food (dental boluses) during mastication. These do not preserve well in most fossil deposits, but at Rancho La Brea, paleobotanical remains survive essentially intact and dental boluses from late Pleistocene forms are amenable to microhistological analysis. Of the identifiable bolus contents, those from Bison antiquus averaged 87% nonmonocotyledons; from Camelops hesternus, 90% nonmonocotyledons; and from Equus occidentalis (one specimen), 56% nonmonocotyledons. A control study on modern Bison bison shows that the boluses contain somewhat lower percentages of monocotyledons than do alimentary samples from the same individuals. However, this accounts for only a part of the very high percentage of nonmonocotyledons in the boluses of the extinct Bison. We conclude that the populations of B. antiquus and C. hesternus represented at Rancho La Brea probably fed little on grasses and that there is enough indirect evidence to suggest that the same may be true for other populations of these taxa. The Equus data are not sufficient to do more than question the usual assumption that Pleistocene horses were always obligate grass eaters.