Grand Gulf State Park

Useful Information

Location: State Hwy W, Koshkonong, MO 65692.
From Mammoth Spring north Highway 63 to Thayer, take old highway 63 through town, turn left on Highway W, follow 9 km to the end.
(36.544073, -91.644807)
Open: All year daily 8-dusk.
Fee: free.
Classification: KarstCollapsed Cave GeologyNatural Bridge
Light: n/a
Dimension: L=1,200 m, VR=40 m, A=217 m asl.
Guided tours: self guided, L=1.8 km, D=45 min.
Photography: allowed
Accessibility: no
Bibliography: Luella Agnes Owen (1898): Cave Regions of the Ozarks and Black Hills, Cincinnati, The Editor Publishing Co., 1898. pp 95-102. gutenberg internat archive
Address: Grand Gulf State Park, Highway W, Box 3554, Thayer, MO 65791, Tel: +1-573-548-2201.
As far as we know this information was accurate when it was published (see years in brackets), but may have changed since then.
Please check rates and details directly with the companies in question if you need more recent info.


1898 described by Luella Agnes Owen in her book Cave Regions of the Ozarks and Black Hills.
1971 designated a National Natural Landmark.
1984 Missouri State Park created.
1986 24 ha portion of the park designated by the state as the Grand Gulf Natural Area.


Grand Gulf is an exceptional and rare karst feature, a spectacular collapsed cave system. A narrow gorge stretches for more than a kilometer with walls almost 40 m high, making the chasm deeper than it is wide. This is not a canyon which was cut into the rock by a river, it is a cave system which formed by groundwater dissolving the limestone. At some point it became big enough for a cave river, the river cave developed by erosion of the cave river. Limestone is dissolved by rain water on the surface, and so the surface lowered slowly and the ceiling became thinner and thinner, and finally it was destroyed and the cave was roofless. This process of becoming roofless started 10,000 years ago, at the end of the last cold age, and goes on until today. There is a short section where the roof is still there, which makes it a natural bridge. The trail at the bottom of the gorge crosses the natural bridge, the arch is 23 m high and 76 m long.

Sometimes the term collapsed cave is used, but a few years ago it was replaced by the term roofless cave. The point is, that there is actually no collapse, no ceiling crashing down. It's not a catastrophic or fast process, it's actually continual weathering, probably small rocks falling down now and then, but it is continuous. And it is ongoing. At the lower end of the gorge or roofless cave, the river vanishes in the open mouth of a cave and flows underground for 14.5 km, finally it re-emerges at Mammoth Spring across the border to Arkansas. So actually there is much more "uncollapsed" cave than "collapsed" cave.

The cave system is not explored, only a short distance inside the passage is blocked by debris and mud. There are cracks which allow the water of Bussell Branch to percolate through, but they are too narrow for cavers. Quite spectacular was a research attempt in the early 1990s, when cavers used a robot vehicle with a camera to enter the cracks, and penetrated some distance into the debris. This unfortunately made clear that the passage is blocked for some distance, which makes any digging futile. The connection of this sink to the huge karst spring SpringMammoth Spring in the homonymous village was proven by dye tracing experiments. It took between 1 and 4 days for the water to reach the spring. And there is still hope that the massive cave system has a side branch or shaft which connects to the surface and may provide an alternative entrance.

This collapse is actually quite recent, it was the result of a severe storm in the 1920s, which washed trees and other debris into the cave, filling the passage. Since then, during heavy rains, a huge lake forms in front of the blockage, which can be up to 30 m deep, and it takes weeks for the water to slowly drain away. 19th century explorers were able to enter the cave. The most famous was obviously PeopleLuella Agnes Owen who describes her exploration of this cave in her 1898 book Cave Regions of the Ozarks and Black Hills, see the excerpt below.

The State Park offers trails along the rim and outlooks, and a trail at the bottom through the natural bridge. Educational signs explain the origin and geology of the site. It's not possible to follow the gorge at the bottom, only a small section has wooden elevated trails. It's also not possible to go to the sink, which is obvious, because the trail would be destroyed by the lake which forms after heavy rains. But the outlook on the southern side of the parking lot offers a good view from above.

The State Park is actually not owned by the government, it is privately owned. The land was acquired by the American timber magnate, conservationist, and philanthropist Leo Drey (*1917–✝2015) from Missouri. The land is owned by the L-A-D Foundation (abbreviation of Leo Albert Drey) which made a long term lease agreement the Missouri Department of Natural Resources in 1984, when it became a State Park.



Luella Agnes Owen

Oregon County, Missouri, is also fortunate in having within its limits the Grand Gulf, which has been declared by competent judges to be one of the wonders of the world; and it offers a combination of attractions that certainly entitles it to an important place among a limited few of America's choicest scenes.

The Gulf is nearly nine miles northwest of Thayer, Missouri, and about equally distant from Mammoth Spring in Arkansas, just a little south of the Missouri state line. The drive is a pleasant one, as the road winds among the forest-clad hills and passes occasional fields of cotton and corn; but having been macadamized in very ancient times by the original and all-powerful general government of that early period is somewhat rough, yet threatens no danger greater than the destruction of wheels.

The only approach to the Gulf is over the hill-tops; and the entrance in past times, while it was still a cave, must have been a sink-hole in the roof of the largest chamber. This chamber is now the upper end of the Grand Gulf, and into it we descended by a rugged path, sufficiently difficult to maintain expectations of grandeur that are not doomed to disappointment. The precipitous walls, two hundred feet in height, bear a faithful record of the energy of circling floods; but instead of frowning, as some good people persistently accuse all noble heights of doing, they seem to look with conscious pride towards the windings of the great rough chasm, where every available spot has been seized on as a homestead for some form of vegetation. All the great, dark rock masses that interfere with easy progress along the lowest depth, were surrounded by a feathery setting of blooming white agaratum; and each turn in the winding course reveals new charms of rock and verdure with their varying lights and shadows until the crowning glory is reached at the Natural Bridge, about twelve hundred feet from the upper end of the cañon. This bridge is magnificent. It was impossible to secure photographs because the abrupt curve by which it is approached gave no point of view for a small camera; and it was equally impossible to reach desirable points for taking measurements, but the open arch is not less than twenty feet wide and considerably more than that in height. From the floor or bed of the Gulf to the road that crosses the bridge is more than two hundred feet. The passage under the bridge makes a curve, the shortest side of which measures exactly two hundred and nineteen feet, and as the width varies from twenty to forty feet, the other side is longer. Most of the floor is flat and level as also is the ceiling, the greatest irregularities being along the wall of greater length which shows at what points the rushing water has spent its force. No water flows through here now except in times of heavy rainfall. The other end of the bridge has a somewhat smaller span but is very handsome, and the outward views from both are exceedingly fine. After traversing about four hundred feet more of the beautiful, high-walled Gulf, we stood before the grand entrance to the cave, which is strikingly similar to the first arch of the bridge. The only picture I was able to get was taken from the slope of the Bridge-crown, one hundred feet below the road, and merely gives a suggestion of the magnificence waiting peacefully for the crowds of eager and enthusiastic sight-seers who will in the near future rush to this charming region in the "Land of the Big Red Apple."

My companions were the same as mentioned in the preceding chapter, a nephew, James Arther Owen, and an obliging, tall young man of twenty, who acted as guide and driver.

Relieving ourselves of all superfluous burdens just within the cave entrance, we lighted candles and sat down to wait for our eyes to adjus themselves to the changed condition, from brilliant sunlight to absolute darkness, broken only by the feeble strength of three candles. It was noticeable that in the moist atmosphere of the Missouri caves, three candles were not more than equal to one in the dry caves of South Dakota.

Very soon we were able to continue the inspection of our surroundings, and the large passage we were in would more properly be called a long chamber, of irregular width but averaging about thirty feet. This ends abruptly nearly five hundred feet from the entrance, but a small passage scarcely more than six feet high runs off at right angles, and into this we turn. It is not quite so nearly dry as the outer chamber, and at a distance of less than one hundred feet we suddenly come to the end of dry land at an elbow of the silently flowing river whose channel we had almost stepped into. The ceiling dipped so we were not able to stand straight, and the guide said he had never gone farther; but to his surprise here was a light boat which I am ready to admit he displayed no eagerness to appropriate to his own use, and swimming about it, close to shore, were numerous small, eyeless fish, pure white and perfectly fearless; the first I had ever seen, and little beauties.

By burning magnesium ribbon we saw that the passage before us was a low arch and occupied from wall to wall by water, the direction of the flow being into another of somewhat greater size at right angles to that by which we had come, and at the mouth of this lay the boat. The distance we could see in either direction was of tantalizing shortness, and the boat was provided with no means of guidance or control, save an abundance of slender twine which secured it to a log of drift from the outside; so I decided to leave my companions in charge of the main coil of twine while I went on an excursion alone, there being not much evident cause for apprehension as no living cow could ever have made the trip to this favored spot.

Although the water looked perfectly placid, the boat drifted with surprising speed, so that the two scared faces peering after me were soon lost sight of. The channel was nowhere more than six feet wide, consequently as the boat inclined to drive against either wall I was able with care to keep it off the rocks with my hands, and in the same way guide it around the sharp turns in safety. After several of these turns there appeared the mouth of a passage so much smaller that the roof was only twelve inches above the sides of the boat and I could touch both walls at the same time. By running the boat across this it was held in place by the current, and I could sit at ease and enjoy the position, which even the least imaginative person can readily conceive to have been a novel one.

The small eyeless fish had been noticeable in the water everywhere but now came swimming about the boat in an astonishing multitude, and as unconscious of any possible danger as bees in a flower garden. Having no eyes, they were naturally undisturbed by the light, so the candle could be held close to the water for a satisfactory examination of the happy creatures.

They bore a striking resemblance to minnows, although a few were larger, and it is claimed that four or five inches are sizes not unusual, but they happened not to be on exhibition. Even dipping a hand into the water in their midst occasioned no alarm, and they might have been caught by dozens.

The guide now loudly called that he had fears of the twine being cut on the sharp edges of rock, and that cutting off all possibility of the boat's return, which being sufficiently reasonable, explorations were indefinitely suspended, and a landing soon made. The camera and flash-light were then prepared for taking a view, and a point of light being needed to work by the nephew was asked to sit in the boat with his candle, to which he readily consented; but judging from the developed picture it may be doubted if his pleasure at the time was extremely keen.

On leaving the cave the guide said it would not be necessary to return to the upper end of the Gulf in order to reach the surface, as the ascent could be made in another place; and leading the way to the left of the entrance he started up the nearly perpendicular wall, more than two hundred feet high, by a sort of "blind trail" that would have caused a mountain sheep to sigh for wings, but it was very beautiful.

We walked over to the wagon road on the high ridge above the middle of the bridge and going down the forest-clad slopes to the perpendicular wall in which is the smaller of the great arches, admired from this fair point of view the marvelous grandeur of one of the greatest natural wonders.

The weather being perfect after a rain the day before, there was no need of haste to get indoors, so we lingered into the afternoon and then drove to the Mammoth Spring, in Arkansas, a short distance south of the Missouri state line, where the Cave River, just visited, comes to the surface in a bounding spring of great force. The distance being little less than nine miles.

The basin filled by the Spring might be called a lake, as its size of two hundred by three hundred feet gives it that appearance, and the color is a remarkable deep blue. The volume of water is so nearly uniform that the height seldom varies more than two or three inches, but three years ago a storm of unusual violence carried out most of the native fish, and in restocking from Government supplies, the clear, cold water suggested an experiment with mountain trout which are found to be doing well.

Where Mammoth Spring flows out its power is utilized by a flour mill on one bank and a cotton mill on the other, and the water flowing on forms Spring River, well known for the charm of its beautiful scenery.

This Spring is described by Dr. David Dale Owen in his First Report of a Geological Reconnoissance of the northern counties of Arkansas, 1857 and 1858, pp. 60-61.

Luella Agnes Owen (1898): Cave Regions of the Ozarks and Black Hills, Cincinnati, The Editor Publishing Co., 1898. pp 95-102.