Rim Rock National Recreation Trail & Beaver Trail. Located in the Shawnee National Forest, Gallatin County, Illinois.
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This cache was located on Shawnee National Forest managed property with permission. Located within the Shawnee National Forest in southern Illinois is Pounds Hollow Recreation Area. This cache makes several stops along two interconnecting trails within Pounds Hollow -- Rim Rock National Recreation Trail and Beaver Trail. The route will lead along the rim of Pounds Escarpment (a circular 50-acre tract of land isolated from the surrounding terrain by steep sandstone bluffs), drop into Pounds Hollow down the sheer 100-foot bluff of the escarpment on a set of stairs, and traverse the base of the bluff back to the parking lot.
Pounds Escarpment, a Pennsylvanian-aged sandstone, is the type locality for the Pounds member of the Caseyville Formation, which underlies the Abbott Formation. The exposure of the Caseyville Formation is considered to be outstanding and significant feature of this site. The Caseyville Formation consists of about 75% sandstone, 10% shale or clay, 5% coal, 5% underclay, and 5% conglomerate. The sandstones are composed of quartz and very little clay and mica. Most contain quartz granules and pebbles, commonly less than half inch in diameter. Secondary enlargement of quartz grains is common and gives sparkle to the rock. The coarser sandstones reach about 100 ft thick and show relatively uniform cross-bedding with dip directions to the west, south, or southwest. (Survey)
Rim Rock lies within the Greater Shawnee Hills section of the Shawnee Hills natural division; one of 14 natural divisions within Illinois. The unglaciated Shawnee Hills form an east-west escarpment of sandstone cliffs and associated rugged topography across the southern tip of Illinois between the Ohio and Mississippi rivers. (Schwegman, 1973) Geology plays a significant role in the topography, associated plant communities and past human usage of this area. The stops along this route will point out all of these interconnected aspects.
Parking: There is a parking area (N37.60195, W088.27804) off of Karbers Ridge Road.
Trailhead: From the parking area, proceed to the trailhead; a short distance you will come to a fork in the trail; follow the right fork part way up the slope to the first stop.
Stop 1: Prehistoric land-use influenced by the geology. (N37.60291, W088.27861) Prehistoric Indians from the Late Woodland (ca. 400-900 AD) were attracted to the unique geology of this and about nine other geologically similar promontories across the Shawnee Hills in southern Illinois. What most of the stone forts have in common is the topography: all are located atop a high bluff on a promontory nearly surrounded by sheer cliffs. Many of the stone forts consist of a stone wall built across a connecting ridge top that serves to block access. The earliest Euro-American explorers (ca. 1807) described the walls as being 6-foot high by 6-foot wide. Artifacts recovered during archaeological excavations at many of the stone forts suggest the walls were used for defense. The stone wall at the Pounds Site is no longer standing, but its tumbled-down remnants can be seen along the southern edge of the sandstone bluff top. One could continue on this trail to the top of the promontory, however, to reach Stop 2 of this cache, please retrace your steps back to the fork in the trail and proceed on the left fork as you face the promontory.
Activity: Notice sparkling, recyrstallized quartz grains in the sandstone bluff. Look at one of the shiny quartz crystals through a hand lens, notice its shape.
Stop 2: The ‘Pounds’ -- how geology impacted land use of early European settlers. (N37.60276, W088.27900) You are now standing at point within a few feet of where the ancient rock wall intersects the cliff face of the escarpment—a good place to observe the transition where the steep cliff-like walls meet the top of the escarpment. Early explorers and settlers referred to the 50-acre escarpment as ‘the Pounds,’ an old English term meaning "an enclosure for sheltering, keeping, confining, or trapping animals." According to Forest Service archival records, timber was logged from the Pounds between 1890 and 1900. Wilson Beasley purchased the land the stone fort is located on in 1855; he purchased 280 acres of land for 13 cents/acre or $35.00! Corn and sorghum were then cultivated on the Pounds during the early part of the 1900s. In 1936 the Civilian Conservation Corps planted a cedar plantation on the abandoned farm field. Since then, native hardwood trees have repopulated the Pounds—they include red oak, white oak, black oak and sugar maple.
Stop 3: Sandstone glade -- a unique landform influenced by geology, topography and exposure. (N37.60321, W088.28061) This sandstone glade is characterized by very steep to vertical sandstone rock exposures along bluffs; is best developed on southern and western exposures and is of Pennsylvanian Period. These bare, weathered rock mantles are evidence of active erosion, which has been hastened by our agricultural land use allowing rapid runoff, trampling of the undergrowth and grazing by livestock, and clearing woodland cover. Drainage on the barren rock is very rapid; they are often ephemerally wet in the winter and spring, becoming dry in summer. Notice how the vegetation is restricted to shelves, cracks, and crevices in the rock where soil or organic matter has accumulated. Trees are sparse, scattered, gnarled, and stunted and extremely slow growing. A member of the blueberry (Vaccinium) family, the farkleberry is almost always restricted to growing on acidic sandstones. Prickly pear cactus (Opuntia humifusa) also grows in this environment. Carpeting the surface of the bare sandstone is a variety of mosses and lichens. (Hill, 2005) (Harris, 1977) As you continue along the trail there are several good overlook spots to experience this interesting plant community. The official trail does not go out onto the bare rock, therefore this cache does not take you out onto it. Should you decide to leave the trail to take a closer look, please take care to not disturb the fragile lichens, mosses and other plants. Please also beware that wet rocks are extremely slick and hazardous and the drop off is very steep.
Activity: Notice the aspect (direction it faces) of this sandstone glade.
Stop 4: Exposed soil layer – the tooth test. (N37.60509, W088.28146) In addition to another good look at the sandstone barren along the cliff top, the small exposed layer of soil here offers a good opportunity for a quick lesson in soil. Soils developed primarily from loess occupy about 63 percent of the states land area. Loess is a silty wind deposit that was deposited during glacial times. Southern Illinois also has rich clay mineral deposits. (USDA-NRCS) Just looking at the soil does not help much in it identification—determining the texture is the key to it ID. Loess has a gritty texture, while clay is smooth. Rubbing a small amount between your fingers might give you a clue, but a surefire way to tell is to put a speck of soil between your teeth. Silt is gritty, clay is not.
Activity: Test the exposed soil to determine if it's loess or clay.
Stop 5: Vertical Joint -- where vertical joints cause giant blocks to separate from the cliff face, forming narrow crevasses. (N37.60653, W088.28045) This stop is an excellent example of vertical joint fracturing common in the Shawnee Hills. Fractures like this were formed in the distant past as a sequence of rocks by the gradual upward bending of the Illinois Basin. The fractures, invisible when buried beneath the weight of hundreds of feet of rock, gradually widen when erosion releases the pressure. Near the surface, water, then roots, penetrating the fracture, combined with steep slope, gravity and sometimes erosion at the base eventually cause wide crevices such the one seen here. (Harris, 1977)
Stop 6: Fat Man’s Misery—how a geologic feature turns into a folk legend. (N37.60683, W088.28001) The wooden platform is a vantage point to view a vertical joint, locally called Fat Man’s Misery. These miseries or squeezes, the result of erosion and time, are narrow crevices within the bedrock and are a common but outstanding feature of the Shawnee Hill. The platform offers a great view of the cliff face and the valley below. Notice the wide variety of plants growing along narrow ledges and tiny cracks of the cliff face and boulders. The next stop is at the bottom of the bluff reached by going down the wooden steps. (If instead you were to continue across the platform the trail continues back to the parking lot through the heart of the Pound.) Take your time as you descend the steps and traverse the narrow fissure. Notice the smooth, weathered, thin-bedded surface with subtle examples of cross bedding on all of the exposed surfaces. The narrow passage leads to the right, then takes a sharp left—looking straight ahead, towards the top of the large block, is an example of chevron slumping. This occurred at the time of deposition when a sequence of thin layers slumped across a stable surface.
Stop 7: Ox-Lot Cave – a geologic feature used as a livestock corral. (N37.60730, W088.28017) Oral history tells us that during the late 1800s logs harvested from the area were rolled or skidded into the hollow where you are now standing. Teams of oxen dragged the massive logs to a tram railroad that ran through the hollow. The 50-some oxen that were used in the operation were kept at night in this large, 20-foot deep by 50-foot wide sandstone bluff shelter at the base of the Pounds Escarpment. The shelter, dubbed Ox-lot Cave, contains a spring that provided fresh water for the oxen. Bluff shelters are shallow cave-like overhangs at the base of a bluff. They are caused when the sandstone layer at the base is less resistant to weathering than the main bluff. Gradually, as the less-resistant layer erodes it undercuts the more resistant layer causing blocks and pieces of the roof to collapse. Although many of the larger bluff shelters in the Shawnee Hills are called caves they are not true caves, as true caves are passages extending into the rock. (Harris, 1977) Find a comfortable perch on one of the large boulders where you can get a good view of the entire shelter and bluff face, as there are several things to see here. 1) A large cross bedding feature can be seen across the face of the bluff. While the sediment was being deposited a large swath was scoured away and filled again to form the cross bedded layer. 2) The base of the bluff is comprised of very thin-bedded, fine-grained sandstone. As this layer erodes the entire bluff slumps down. 3) There are three distinct colors on the bluff face—the reddish brown is iron oxide, the black is manganese iron oxide, and the white blotches are lichens. 4) Rising directly above the spring on the right side of the shelter you can see a tall vertical joint; most likely the source of water for the spring. The moist sandstone and soil near the spring support a lush population of thalloid liverwort (Conocephalum conicum).
Stop 8: Pounds Hollow – a stream valley named for the Pounds Escarpment. (N37.60777, W088.27872) Cradled between sandstone bluffs in every direction, the valley floor is a floodplain of a low-gradient rock-laden intermittent stream. A rich ravine forest is dominated by beech, sugar maple, tulip tree and red oak, with an understory abounding with wildflowers, especially during spring. A half-mile side-trip downstream will take you to Pounds Hollow Lake—return to this spot to continue on the trail around Pounds Escarpment for the next geology stop.
Stop 9: Vertical Fissure – another great example. (N37.60672, W088.27824) Peer back over your right shoulder for another great example of a massive vertical fissure. Notice the striking difference in texture and color of two sides of the fissure.
Activity: Think about what chemical compound along the face of the smooth layer gives it a reddish color.
Stop 9: Sandstone boulder – the origin of ‘rock n’ roll’? (N37.60606, W088.27775) This giant rock, standing alone on the opposite side of the trail from the bluff, is a geology lesson all by itself. The rock, once part of the bluff, over time separated to form a wide joint, which widened into a crevice, and eventually slid and tumbled away from the cliff face to its current position. (Harris, 1977) Take a close look at the features on the surface of this rock. Notice the numerous small, smooth, white quartz pebbles and the sparkly recyrstallized grains of quartz scattered all over. Another intriguing feature is the boxwork--irregularly shaped pockets lined with iron oxide. This phenomenon is caused by concentrations of iron oxide along intersecting joints. Later, when erosion exposes the rock near the surface the more resistant iron oxide cemented portion remains while the more poorly cemented sand grains are washed away.
Stop 10: Movement of rocks – how position, shape, color and even graffiti give clues about the rocks we see. (N37.60418, W088.27685) From this stop look across to the bluff at the jumbled pile of rocks and boulders that have collapsed below the bluff. Notice how much lighter in color and more angular in shape these rocks are than others you’ve seen along the trail. These clues tell us that these rocks have not been on the ground enduring the weathering processes as long as other rocks we’ve seen. While it’s difficult to tell just how long ago this collapse took place, we know it took place prior to the oldest graffiti on the face of the bluff!
Activity: As you continue up the trail notice the smaller, broken rocks covering the steep hillside on your left. Relative to other rocks, these rocks are moving down slope pretty fast.
Stop 11: End of the bluff – beginning of the prehistoric rock wall. (N37.60308, W088.27772) If you carefully peer through the trees you can see the point where the sheer bluff gives way to a gentler slope and where the prehistoric rock wall begins.
Activity: Consider where the Indians may have gotten all the rocks with which they built the wall.
Works Cited:
Harris, S. E. (1977). Exploring the Land and Rocks of Southern Illinois. Carbondale, IL: Southern Illinois University Press.
Hill, S. R. (2005). Conservation Assessment for the Limestone and Sandstone Cliff and Talus Communities of the Shawnee and Hoosier National Forests, Illinois and Indiana.
Illinois Natural History Survey, Center for Wildlife and Plant Ecology. Champaign: Illinois Natural History Survey.
USDA-NRCS. Retrieved 2011-08-10 from Technical Resources: http://www.il.nrcs.usda.gov/technical/soils/soilsofil.html