Heavener Runestone State Park

Introduction to Project Site
The Heavener Runestone State Park is located in eastern Oklahoma near the town of Heavener in Le Flore County. The runestone itself is an erratic sandstone block Pennsylvanian in age. The bedrock in the state park is all sandstone underlain by shale of the same age. The sandstones create the valley’s caprock around its perimeter, with the shale underneath. Many large sandstone blocks have fallen from what could conceivably have been a “ceiling” over the valley, creating potentially a large, attractive shelter. Some of these smaller shelters still exist in the valley wall and underneath some of the fallen sandstone blocks, also known as talus, and should be investigated for possible runes on the sandstone blocks that are forming these small shelters and talus caves, while many others, probably larger, most likely existed years ago but collapsed over time, evidenced by the many large sandstone blocks visible throughout the valley’s floor.

Gloria Farley had provided signed documents suggesting the existence of a cave near the runestone. Two of these documents suggested the cave was rather extensive, extending into the hillside. One, which surfaced recently, suggested the cave was a 40-foot by 20-foot by 8-foot shelter near the runestone. It is also stated that the shale was washed out, or eroded out, producing the void space in the shelter. I believe this to be true. Unfortunately, it would be extremely difficult, if not impossible, to have an extensive cave system existing through the hillside, as that would require a type of rock that would succumb to chemical weathering, like limestone or dolomite, both of which are not present in the vicinity of the park. Microgravity data collected below the picnic shelter above the cliff, in the parking lot, and along the entrance road supports this. But, it is very reasonable to believe that there was a void space, or a shelter cave that existed at the very location where the park’s sign suggests it did exist. This is not only reasonable to believe due to the probable geologic history of the area, but the microgravity data does suggest a void does exist at that location.

Results of Microgravity Data
The following is a written description of each set of data collected. For simplicity, each set of data have the following names: 1) parking lot line, 2) clifftop line, 3) road line, and 4) cliff line.

Parking Lot Line
The parking lot line was established to cover the length of the parking lot where it was suggested a cave passage may exist, between the valley where the opening is said to have existed, and the residential home adjacent to the parking lot, opposite the visitors’ center. This line was 400 feet long, and dropped 34.4 feet from the upper end of the parking lot to the lower end. This line shows a number of very small anomalies which correspond to the locations of buried pipes and utilities. The gravity data drops drastically near the end of the line, and this is completely due to the existence of the valley at the lower end of the line. There is no cave-type anomaly suggested by this data set.

Clifftop Line
The clifftop line was established with the intent to possibly visualize a cave passage that may not have made it to the parking lot, but still eroded its way into the hillside. This line was 230 feet long, and its vertical range was 12.4 feet. Data along this line shows the existence of a number of “cutters” which I am interpreting to be enlarged fractures, or joints, in the rock. To visualize these joints, think of the large cracks that still exist in the sandstones and shales near the cliff, where water prefers to flow. It is evident from site evaluations that the rocks in the area have a joint or fracture pattern, and some of these fractures are rather large, like the ones near the cave sign. A cave-type anomaly would have more of a bowl shape to it, especially since we had established stations every ten feet. Thus, no cave-type anomaly is suggested by this data set.

Road Line
The road line was established for two reasons. One was to test the theory that the cave may be the source of some of the depressions and small stream features visible at this point in the entrance road. The second was to delineate what the possible cause of subsidence is along the entrance road, and how large an area is potentially affected. This line was 330 feet long, and dropped a total of 33.2 feet. Again, there are a number of cutters located throughout much of this line, once again suggesting the existence of larger fractures in the rock. The road subsidence is near the lower end of the line, and there is an isolated cutter located at station 28. This appears to be the only potential culprit for the subsidence along the road related to processes underground. Because of the nature of the rocks in the area, and the existence of these fractures, it is reasonable to consider that some of the fill material that was used to support the road may be filling into some of these fractures, explaining the lack of cutters before and after station 28. This could be causing the road to slowly lose support. There is also a possibility that due to the drainage pattern along the road, that rain water traveling downhill is also eroding away some of the support for the road on the valley side (north side) of the road. Most likely it is a combination of the two factors. I feel that this subsidence will be minimal, and that tearing up the road to replace potentially lost fill material would maybe cost more than doing periodic repairs to the road. No cave-type anomaly was interpreted along this line.

Cliff Line
This line was established at the base of the cliff, at the location where the cave entrance is suggested to have existed. This line was unique from the others for a couple of reasons. First, the previous lines all used a station spacing of ten feet. This line had a station spacing of five feet. This change was made because the material that now exists at this site is all loose, broken material that is very unconsolidated. In order to distinguish between larger voids in this loose material and a possible buried cave entrance or shelter, it was necessary to increase the resolution by changing the station spacing. Secondly, this line was much shorter since we had a good idea of where the cave may be. This line was 70 feet long, and fluctuated in elevation by only 1.4 feet. Finally, this line is unique from the others due to the cave- type anomaly suggested by the data. This cave-type anomaly exists around, and includes, stations 9 and 10, and is a 60-microgal anomaly. The other anomaly centered around station 4 is most likely another cutter or fracture zone and seems more pronounced due to the five-foot station spacing. The cave-type anomaly was modeled based on the dimensions suggested in the letter describing a shelter-like erosional cave that had dimensions of 40 feet long by 20 feet by 8 feet high. This model (figure 6) suggests that a void of the above dimensions will create a 60-microgal anomaly at a depth of approximately 20 feet. Please keep in mind that even though we have had great success in locating caves with this method, that this is still not 100% guaranteed, but it is one of the most effective methods that can be utilized to locate voids beneath the earth’s surface.

Statistical Evaluation of Data
Regionalized variable analysis (geostatistics) can be used to assess the confidence of the gravity data. Spatial variograms, which model the variability changes with distance, are used to produce kriging estimates for each known data point. These estimates are based on all of the gravity data except for the known point. A comparison of the estimated versus known data points (see figure 7) indicates the gravity data is reproducible and robust. The variogram also allows us to assign a degree of confidence to any estimates of gravity made outside surveyed areas. We can feel comfortable that our assessment of the gravity trends along these lines is reproducible.

Conclusions and Recommendations for Future Investigations
The data does suggest that a sizeable void does exist at the cliff base. This does support the information that a cave or shelter had existed at the site. The other lines do not suggest anything that would warrant further investigation. I do not believe that there will be any additional runes on the walls of the void space since the walls would most likely have been shale, which would easily erode and not support markings for any longer period of time. There could be sandstone blocks in this void, or supporting this void that could contain runes. There is also the potential for artifacts to be found in this void if it were used by people in the past.