Well-dated syntectonic unconformities with the Spanish Pyrenees allow characterization of sedimentation and deformation within an orogenic foreland. The Spanish Pyrenees are composed of a south-vergent thrust belt and foreland basin in which folds developed both parallel and perpendicular to tectonic transport. Unconformity geometries and magnetostratigraphic data from synorogenic strata provide a precise temporal framework for the quantitative analysis of the Mediano anticline, the largest of the transverse folds. Folding began in the early Eocene and ended by ∼42 Ma at which time an anticline 20 km long and ∼5 km in wavelength had been produced. Angular and progressive unconformities within syntectonic sedimentary units preserve the history of fold development. Fold growth resulted from west-ward salt movement driven by prograding sediments and was characterized by 2-3 m.y. intervals of slow continuous limb tilting, 2.2°-4.2°/m.y., preserved as progressive unconformities within syntectonic strata. Because the emplacement of the Cotiella-Montsec thrust sheet was episodic, intervals of slow fold growth were punctuated by intervals lasting <1.5 m.y. when fold growth was three to ten times faster, producing angular unconformities.