Spring Valley Caverns



Holy Grail Cave, located in S.E. Minnesota, was discovered in 2008 after a rare catastrophic supercell rain storm collapsed the roof of a tall dome. Explorers rappelled 50’ down into the cave and went on to discover possibly the largest rooms, passages, pits and domes in the Tri-State region. It is thought that this cave is part of the huge York/Odessa underground drainage system that explorers have been attempting to enter since the 1800’s. To date 4 miles of passages have been explored, and cavers are searching for the connecting passage that may lead them into the York/Odessa drainage system. It is estimated that this system may contain over 50 miles of cave passages. The Minnesota Cave Preserve owns 11 surface acres above the caves only entrance, and 148 acres of subsurface rights to this complicated cave system.

Download the STORY

View the MAP

Read the HISTORY


Supercell Rain Event
Click for larger view

On June 7th, 2008 a catastrophic supercell rain event, which spawned brief hail, tornadoes and damaging winds, hit Fillmore County. Eleven inches of rain pounded down in a short period of time, which caused significant flooding. Major roads were closed, and the nearby town of Granger, located along the Upper Iowa River, was surrounded by water.

From devastation came exuberance! Sometime later John Ackerman received a phone call from Dan Dornink, a fellow caver, lifelong resident of the area and Fillmore County Sheriff’s Deputy. He described a gaping hole that had opened up during the storm event in a farm field, along the York/Odessa corridor. Dan suggested that John bring the full caving arsenal.
Opened Hole
Click for larger view  
Odessa Spring
Click for larger view
We know that a major cave system exists, beginning from the largest blind valley in Minnesota (The York Blind Valley) and ending 10 miles away, at the largest spring (Odessa Spring) in Minnesota. Dye traces conducted by Dr. Calvin Alexander have shown that water from 12 square miles drains into the York Blind Valley. Dye tracing has also proven that this water meanders through the earth until finally discharging from Odessa Spring, located at the base of a magnificent limestone cliff along the Upper Iowa River. (Along the Minnesota/Iowa border.) This 2001 photo shows Matthew Ackerman at Odessa Spring.
John Ackerman and Clay Kraus peer into the newly collapsed hole. This site is about 4 miles from the York Blind Valley, right along the suspected underground corridor which stretches into Iowa. Since the 1800’s explorers have attempted to find this fabled underground cave system. Could this be it?
Click for larger view  
First Time
Click for larger view

The open abyss was found to be 50’ deep. While Clay, Dan and Dave Gerboth were engrossed with a lead near the entrance shaft, John Ackerman explored in the opposite direction. John located a tiny crack along the edge of a narrow low passage with wind blowing out from beyond.

John removed loose soil, sand and rocks, and worked his way upward, following a tiny void. Soon he saw open blackness and climbed up into a large room. He walked around the room but could not locate the continuation, so again he searched for the wind source. Again John noted a crack along the floor and dug up into a spacious passage. He followed the passage for several hundred feet and encountered a stunningly huge intersection - open blackness could be seen in both directions. He retraced the route back, regrouped with Clay, Dan and Dave, and together they explored beyond John’s turn around point.

Discovery Route
Click for larger view  
First Big Room
Click for larger view
We turned the corner and found this! Could we have discovered the York/Odessa Cave System?
It was immediately apparent that this newly discovered cave be protected. This open sinkhole needed to be capped. Not only was it a serious liability issue, it was also a hungry monster, just waiting to swallow tons of fertile black soil from the surrounding fields during heavy rain events. Even though the sinkhole was on private property the Minnesota Cave Preserve felt the need to step forward and spearhead this project. This photo shows the placement of structural tube beams over the hole.
Closing Hole
Click for larger view
Temp Access
Click for larger view  
Thick plywood was placed over the beams and rebar was installed. Sheets of tin were placed along the perimeter to form a tight seal. A temporary access to the cave was installed.
High strength concrete was poured over the works.
Concrete Poured
Click for larger view
Click for larger view  
The site was backfilled and a culvert extension was added. The 4 owners of the property (Ed, Glenn, John & Kay Ivers) were supportive of John’s quest to preserve, study and protect this unique underground wilderness. They subsequently sold John 11 surface acres and 148 acres of subsurface cave rights.
A new entrance will be installed in a more appropriate location (approx. 400’ northeast of the original entrance) on John’s newly purchased land, and this temporary entrance will be removed.
Temp Entrance
Click for larger view
Test Hole
Click for larger view  
A specialized rig bored a small diameter hole down into the cave to verify the accuracy of the new 30” diameter shaft. The original sinkhole site remains the property of the Ivers.
The new entrance was created by this drill rig.
Drilling shaft
Click for larger view
Filming breakthrough
Click for larger view  

The actual breakthrough was filmed from inside the cave-a never before filmed event.
Point your browser here to watch the breakthrough:

Javier Guzman stands at the new entrance into Holy Grail Cave, which is 65 feet below the surface.
New Entrance
Click for larger view  
Clay Kraus
Click for larger view  
As the cave is explored it is surveyed. A map is then created and the surface features are superimposed on the final draft.
We have discovered possibly the largest rooms, passages, pits and domes in Minnesota.
Twin Passage
Click for larger view  
Click for larger view  
To date over 4 miles of cave passages have been discovered.
Ninety seven percent of the cave lies under the land that is protected by John’s (Minnesota Cave Preserve) subsurface rights.
Huge Passage
Click for larger view  
Ancient Room
Click for larger view  

Explorers continue to search for the passage that may connect to the vast York/Odessa Cave System. If discovered, it is estimated that the entire cave system could contain more than 50 miles of cave passages!

In June, 2009 fluorescein dye was poured amongst droplets that continually fall to the cave floor in this room. Within several weeks the dye was picked up and identified by special receptors at the Odessa Spring resurgence. Positive proof has now been established that this cave lies directly over the York/Odessa drainage system.


Numerous deep pits have been discovered, and some contain water of unknown depths. Several such pits were rigged with ropes, and one explorer (John Ackerman) descended down into the depths in a wet suit to investigate. It is hoped that cave divers can probe these water filled pits and find a conduit which could lead directly into the extensive York/Odessa System.
Deep Pit
Click for larger view  

Holy Grail Cave History