Is third from lowermost member of Hornbrook Formation. Named for outcrops adjacent to Ditch Creek about 3 km west of Hornbrook. Type section designated in road cuts along northbound lane of HWY I-5 about 3 km south of Hornbrook, NE/4 NE/4 sec.32 T47N R6W, Hornbrook 15' quad, Siskiyou Co, CA. Dominantly gray siltstone with interbedded silty very fine-grained sandstone; locally contains mudstone and fine-grained sandstone in lower part. Generally 20 to 80 m thick (62 m thick at type). Conformably overlies Osburger Gulch Sandstone Member (new) (Hornbrook Formation) except in Ashland area where it unconformably overlies basement rocks. Contains locally abundant molluscan fossils including ammonites, pelecypods, gastropods, and foraminifers. Age considered Turonian and Coniacian (Late Cretaceous).

Source: GNU records (USGS DDS-6; Menlo GNULEX).

Detailed lithology includes coal bed near Hagedorn Ranch adjacent to Yreka-Ager Road about 4.5 km southwest of Willow Creek School, SW/4 SW/4 sec.24 T46W R6W, Copco 15' quad, Siskiyou Co, CA. Measured type section, lists of fossils, depositional environment, and mapping included in study. Age of unit in its main outcrop ranges from early Turonian to early Coniacian based on included fossils.

Source: GNU records (USGS DDS-6; Menlo GNULEX).