Johnson's Shut-Ins State Park attracts about 250,000 visitors annually, but Wednesday's failure of a reservoir has shut down the park down until further notice.

"Preliminarily, from the reports we got yesterday, there has been extensive damage to Johnson's Shut-Ins," Sue Holst, spokeswoman for the Missouri Department of Natural Resource's parks division, said Thursday.

The water plant house, which held the equipment that supplied water for the park, was gone. Pedestrian boardwalks suffered damage, and it was believed there was damage to the Ozark Trail. A park store sustained water damage, Holst said.

A team of about eight people, including engineers and a risk management official, were assessing the extent of the losses.

Holst said 19 campground reservations for 44 nights in the park had been canceled, and those who booked to stay at the park will receive full refunds. The park will not accept new reservations until it becomes clear when it can reopen.

Johnson's Shut-Ins got its name thanks to the mix of geology and water in the area.

About 1.5 billion years ago, hot volcanic ash and gases spewed into the air, then cooled, forming a type of rock produced under conditions of intense heat, called igneous rock.

Over time, water from the Black River became confined, or "shut-in" to narrow channels, leading sand and gravel carried by the waters to cut into the erosion-resistant rock and resulting in dramatic chutes and gorges.

Much of the park was donated to Missouri in 1955.

The roughly 8,550-acre park offers camping, fishing, swimming, backpacking and hiking and horse trails. Holst said there were no reservations booked for the night before the breach, typically a quiet time of year for the park.

Officials and frequent park attendees said there's no question the reservoir breach could have been a much worse disaster, had the rupture occurred during a busy time at the park.

"Everyone's wiping their brow, and saying, 'Thank God it didn't happen on a summer weekend,"' said Richard Orr, 55. He works as a senior camping buyer for The Alpine Shop in the St. Louis suburb of Kirkwood and has been visiting Johnson's Shut-Ins for a half-century.

While it was sad to contemplate the damage, Orr found some relief in knowing the natural wonder of the shut-ins should remain.

"We're comforted by the fact that the rocks are almost eternal, and won't be affected," he said.