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Over the past 40 years, observational surveys have established the existenceof a tight relationship between a star's age, rotation period, and magneticactivity. This age-rotation-activity relation documents the interplay between astar's magnetic dynamo and angular momentum evolution, and provides a valuableage estimator for isolated field stars. While the age-rotation-activityrelation has been studied extensively in clusters younger than 500 Myr,empirically measured rotation periods are scarce for older ages. Using thePalomar Transient Factory (PTF), we have begun a survey of stellar rotation tomap out the late-stage evolution of the age-rotation-activity relation: theColumbia/Cornell/Caltech PTF (CCCP) survey of open clusters. The first CCCPtarget is the nearby ~600 Myr Hyades-analog Praesepe, where PTF has producedlight curves spanning more than 3 months and containing >150 measurements for~650 cluster members. Analyzing these light curves, we have measured rotationperiods for 40 K & M cluster members, filling the gap between the periodspreviously reported for solar-type Hyads (Radick et al. 1987, Prosser et al.1995) and for a handful of low-mass Praesepe members (Scholz et al. 2007). Ourmeasurements indicate that Praesepe's period-color relation undergoes attransition at a characteristic spectral type of ~M1 --- from a well-definedsingular relation at higher mass, to a more scattered distribution of both fastand slow-rotators at lower masses. The location of this transition is broadlyconsistent with expectations based on observations of younger clusters and theassumption that stellar-spin down is the dominant mechanism influencing angularmomentum evolution at ~600 Myr. In addition to presenting the results of ourphotometric monitoring of Praesepe, we summarize the status and future of theCCCP survey.

The Age-Rotation-Activity Relation: From Myrs to Gyrs