Abstract Gutenberg is a picturesque community nestled in the Mississippi River Valley, where local relief approaches 400 ft (120 m). Lock and Dam No. 10 at Gutenbergis a major conduit for upper Mississippi barge traffic. Visitors can view the lock in operation at close range from an observation platform. Excellent roadcuts and many additional exposures of Middle Ordovician strata are easily accessible in the Gutenberg area, where virtually every bed is available in continuous fresh exposures over a stratigraphic interval of more than 250 ft (75 m).Three reference sections (Fig. 1B) enable the sequence of Ordovician formations (St. Peter, Glenwood, Platteville, Decorah, Dunleith, Wise Lake) to be composite for general discussion (Fig. 2) :1) Gutenberg South Roadcut, US. 52 (SW¼Sec.29, T.92N., R.2W.), a superb continuous section that offers a spectacular view of the Mississippi River (Delgado, 1983); 2) Gutenberg North Roadcut, U.S. 52 (SW¼SW¼Sec.5 and NW¼Sec.8, T.92N., R.2W.), a well-studied but now partly overgrown sequence (Templeton and Willman, 1963; Bakush, 1985); and 3) X56 Roadcut, Great River Road (NW¼NW¼Sec.32 and SW¼SW¼Sec.29, T.93N., R2W.), a similar sequence to Gutenberg North, but better exposed by recent road construction. Excellent exposures of Lower and Middle Ordovician rocks are also accessible at Clayton (especially private barge terminal road) and the Pikes Peak State Park area (Fig. 1A). Good exposures of Jordan Sandstone (Cambrian) can be seen along the river from McGregor north to Effigy Mounds (Fig. 1A). Ordovician stratigraphic terminology in