Grand Gulf State Park is a state-operated, privately owned and publicly accessible, geologic preserve near Thayer, Missouri, United States, encompassing a forked canyon that is the remnant of an ancient collapsed dolomite cave system. The land that is now the park was acquired by conservationist Leo Drey (1917–2015) before becoming part of the Missouri state parks system. The 322 acre state park has been operated by the Missouri Department of Natural Resources under a lease agreement with the L-A-D Foundation since 1984. Grand Gulf was declared a National Natural Landmark in 1971 as an excellent example of karst topography and underground stream piracy. A 60 acre portion of the park was designated by the state as the Grand Gulf Natural Area in 1986.

Description

The Grand Gulf is nearly 1 mi long and up to 130 ft deep with sheer sides. An uncollapsed part of the original cavern roof spans 250 ft, creating one of the largest natural bridges in Missouri. A watershed of 28 sqmi feeds into the gulf which itself drains into a cave entrance at its eastern end. Dye traces have shown that water entering the cave in Grand Gulf emerges 1 to 4 days later at Mammoth Spring in Arkansas, 9 miles (14 km) distant.

Facilities

The park has picnicking facilities and two trails for viewing the gulf. The park's heavy foliage makes fall and winter the best viewing seasons.