Abstract: Petrological and geochemical studies of Late Jurassic volcanic rocks in the Tiaojishan and Houcheng Formations in northwestern Hebei Province reveal that Late Jurassic volcanic rocks are composed mainly of a shoshonite series derived from the enriched mantle, and some high-potassium acidic rocks of crustal affinity. Overlying the Tiaojishan Formation, the Houcheng Formation consists primarily of fluvio-lacustrine rock associations and is believed to have deposited in rifted basins in an extensional setting. It is marked by coarse-grained sediments of alluvial fans and braided rivers in the lower part and fluvio-lacustrine fine-grained sediments intercalated with volcanic rocks in the upper part, thus generally exhibiting an upward-fining sequence. The stratigraphic and sedimentary evolution from the Tiaojishan to Houcheng Formations reflects the transition from a down-faulted basin to a downwarped basin. Regional compression occurring after the deposition of the Houcheng Formation led to the reversion of the extensional basin of this stage.