Illustration of an oreodont — in this case a merycoidodon, similar to those that populated the SCV for 30 million years (until ~4.9 MYA). Artwork by Heinrich Harder (1858-1935). Oreodonts were hog-like ruminants. This illustration and the map below are not part of Whistler's paper. Click to enlarge.

In 1940, Richard H. Jahns reviewed the stratigraphy of the nonmarine Mint Canyon Formation in the eastern part of the Ventura Basin and separated from it a new formation and fauna. Previous to this work, a controversy existed as to the age of the Mint Canyon Formation, for it contained vertebrates considered indicative of both the Miocene and Pliocene (Kew, 1924, Maxson, 1930, and Stirton, 1933). As a partial solution to this controversy, Jahns demonstrated the presence of an erosional unconformity low in the nonmarine sequence which indicated a shift in source area. He redefined the beds below the unconformity as the Tick Canyon Formation (Jahns, 1940, pp. 163-66).

The composite Tick Canyon fauna as presently known is as follows: a heteromyid rodent, Trogomys rupinimenthae Reeder, 1960, a rabbit, Archaeolagus acaricolus Dawson, 1958, two oreodonts, Merychyus (Merychyus) calaminthus Jahns, 1940, and Merychyus (Merychyus) jahnsi (this paper), a camel, Miolabis californicus Maxson, 1930, and a stenomyline camel (previously unpublished record).

All California Institute of Technology collections are now conserved in the Los Angeles County Museum of Natural History. With the consent of this institution, the author was able to study the entire sample of oreodonts from the Tick Canyon fauna, which includes an additional maxillary fragment collected by Miss Beth Chasse, an associate of the museum.