Grand Gulf State Park is a state-operated, privately owned and publicly accessible, geologic preserve near Thayer, Missouri, 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 the late conservationist Leo Drey (1917–2015) before becoming part of the Missouri state parks system. The 322acre 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 60acre portion of the park was designated by the state as the Grand Gulf Natural Area in 1986.DescriptionThe Grand Gulf is nearly long and up to 130ft deep with sheer sides. An uncollapsed part of the original cavern roof spans, creating one of the largest natural bridges in Missouri. A watershed of 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.
