Lying in southeastern California between Indian Pass and Picacho State Recreation Area is the ~440 m thick, Jurassic Winterhaven Formation. This unit has been metamorphosed to chlorite-grade greenschist facies and can be divided into a lower metavolcanic member and an upper metasedimentary member. The Winterhaven Metavolcanic Member can be subdivided on the basis of texture into coarse grained (Group 1) and fine grained (Group 2) variants. Group 1 samples are found only east of Little Picacho Wash, while west of this divide 8 out of 10 samples belong to Group 2, while the remaining 2 belong to Group 1. The spatial variation in grain size suggests that lava within the Winterhaven may have flowed east to west. In this study, the physical and chemical properties of each major textural variant were evaluated. The LREE and HREE depletion patterns for both groups indicate small degrees of partial melting within the garnet-stability field. The consistency of the REE distribution patterns suggests that all samples came from the same general source. The REE distribution patterns of the Winterhaven Metavolcanic Member and Miocene Quechan Volcanics are almost identical, both exhibiting LREE enrichment and HREE depletion patterns. However, samples of the Winterhaven Formation consistently plot above those analyzed from the Quechan Volcanics. Such a relationship suggests that the subcontinental crustal mantle may have been depleted in the REE during the petrogenesis of the Winterhaven Formation and/or the Quechan Volcanics involved a lower degree of partial melting during their petrogenesis.