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Grand GulfAfter heavy rains, a deep pool of water fills the canyon at Grand Gulf near Thayer.
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Grand Gulf 2When water drains out of the pool, the canyon reveals rocks that were once part of te original cave system's roof.
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Grand Gulf 3A boardwalk leads visitors down to the canyon.
More than 10,000 years ago, the roof of a cave system collapses in the lower ozarks of southern Missouri and created Grand Gulf, a deep canon that is almost a mile long with walls almost 130 feet high. The canyon, located in the 322-acre Grand Gulf State Park near Thayer, is a true chasm, meaning it's deeper than it is wide, and it's known as the Little Grand Canyon of the Ozarks.
The geologic curiosity was formed more than a million years ago by limestone and dolomite bedrock that dissolved in the area's slightly acidic groundwater. The water seeped into fractures and fissures in the bedrock, and over time, as the rock eroded, those cracks grew larger and eventually turned into a system of caves. The rock continued to rerode, weakening the roof of the cave system until it collapsed and formed Grand Gulf.
A surface creek that drains about 25 square miles empties into the chasm and passes under a 250-foot-long natural bridge, a remnant of the original cave's roof. The bridge is 50 feet wide, 27 feet high on one end, and only about 10 feet high on the other.
Visitors can hike a trail that leads across the bridge for a view down into the canyon, where tumbled dolomite blocks that were once part of the cave's roof can still be seen.
The canyon's depth increases as the water in the creek moves downstream. At the end of the chasm, the water enters the mouth of the remaining underground cave system, travels about nine miles, and reemerges at Mammoth Spring, Arkansas. Geologists determined that where the water goes by adding dye to the water that flowed into Gran Gulf's cave. The dyed water returned to the surface at Mammoth spring a day later.
At the downstream end of the chasm, mud and debris block the intact mouth of the original cave, preventing human entry. In the early 1990s, a robot vehicle equipped with a digging tool and a remote camera was sent into the mouth. The robot revealed massive blockage inside. But this wasn't always the case. In her 1898 book Cave Regions of the Ozarks, geologist Luella Agnes Owens wrote about exploring Grand Gulf. She describes using a small boat to tour the underground cave system and seeing "numerous, small, eyeless fish, pure white and perfectly fearless."
The deeper portions of the cave were accessible until the 1920s, when a severe storm passed through and filled the mouth of the cave with downed trees and other debris, slwoing the natural drainage underground. Today, heavy rains fill the gulf to depths exceeding 100 feet, and it can take several weeks for the water to drain out of the canyon.
Grand Gulf was designated a National Natural Landmark in 1971, and it became a Missouri State Park in 1984. The park features hiking trails, picnic sites, and a boardwalk that descends into the canyon. Coming back out of the canyon requires climbing many fligths of stairs, but the sight of this geologic wonder is worth the huffing and puffing.