The upper Eocene-lower Oligocene Keasey Formation in northwestern Oregon consists of ~700 m of deep marine forearc basin sediments exposed in stream beds and roadcuts. The abundant molluscs of this unit were the basis for the Keasey Stage of the Weaver et al. <1994> timescale, but the precise age of this fauna and formation have long been controversial. Analysis of over 130 magnetic samples from the Keasey in five sections yielded a stable remanence held mainly in magnetite which passed a reversal test. On the basis of calibration by benthic foraminifera and molluscs the Keasey Formation is correlative with Chrons C15r-C12r (35.0--33.0 Ma), so the unit spans the latest Eocene and early Oligocene. The magnetic directions suggest a tectonic rotation of 73.7¿¿4.7¿, which is consistent with rotation of the nearest volcanic basement rock reported by Wells and Coe <1985>.