Trail Section 14 - Falls Lake Trail Geologic Guide


Geologic Map Trail Section 14-15

Geologic information by Edward F. Stoddard (in Bold Text).

Mileage and Trail section descriptions from Mark Edelstein with updates from March – April 2011.


Section 14 (Rolling View to Little Lick Creek)

37.7 – After passing by the entrance station to Rolling View, reach a yellow manhole cover and turn L to reenter the woods.

37.9 – Cross a small creek bed. Soon junction, L, with a blue blazed path to a hiker’s parking lot off Baptist Road.  [If you take this trail toward the parking lot, you will cross a gully with an outcrop of coarse red sandstone.  Upstream in the same gully there are large angular blocks of metadiorite.  They came from a rock quarry on Westgate Road in Raleigh near RDU Airport, and were placed here during construction of the park’s water treatment facility, located just above here.]  Shortly after this, pass through a low-lying, wet area.

14-A:  Here you enter the relatively wide floodplain of a relatively narrow creek.

38.1 - Cross a small creek bed.

38.2 – Cross another small creek bed in a low-lying section.

14-B:  Here you begin to encounter pieces of diabase along the creek and trail.  As you go up the hill, the diabase pieces become more abundant, larger, and fresher.  The true position of the diabase dike is along the uphill limit of the loose pieces; you may even see an outcrop here.  In fact, the trail is going around a ridge trending about N25°E.  The diabase dike probably supports the ridge.  Pieces that are broken from the dike can be weathered and roll downhill, but not up.  Unless someone has moved the loose rocks, geologists use the uphill limit as a guide to the true location of the bedrock.

38.3 – Cross a small creek (May be dry).

14-C:  Here, in the trail and down to the right, is an outcrop of medium-grained reddish-brown sandstone.  We are in the outer part of the alluvial fan, near the transition to river deposits.

38.4 – Junction with an unmarked path, L.

38.6 – By the top of a rock face cross a small creek.

14-D:  Here the trail crosses a small creek with a six-foot high waterfall.  The rock is pebbly sandstone containing pieces of igneous and metamorphic rocks eroded from the region east of the Jonesboro fault.  Look closely, and you may see that the pebbles don't touch each other, but instead are surrounded by fine sediment - silt and clay.  Such matrix-supported sandstones result from slurry flows, like mudflows but with slightly more water.  These are typical deposits in alluvial fans.

38.7 – After a slight ascent, reach lake views, R. Soon pass through piles of trees cut to allow passage of the trail.

14-E:  At this point the trail crosses a prominent diabase dike trending about N30°E.  You can trace the boulders through the woods on both sides of the trail.  Note that some of the boulders are beginning to take on the rounded shape typical of spheroidal weathering.

14-F:  Below to the right you can see that the lakeshore has a smoothly curved shape.  This is an old meander loop of the Neuse River.

39.2 – Near the lakeshore turn L to walk up some steps and pass by several residences. The trail becomes narrow through here.

14-G:  If you go down to the lakeshore here, and assuming the lake level permits, you will be treated to a very nice long cliff exposure of Triassic sedimentary rocks.  You can see coarse, poorly bedded pebbly sandstone that grades upward into finer reddish siltstone near the top of the cliff.  Below the sandstone, there is more reddish siltstone, and if the water is low you will see another sandstone bed at the waterline.  Note that the sandstone is much more resistant to erosion than the siltstone, and thus forms a prominent ledge here.  Wave erosion preferentially affects the softer siltstone, and thus undercuts the sandstone ledges, resulting in the huge blocks along the beach.  These rocks constitute two fining-upward sequences that are more typical of river deposition than alluvial fans (Figure 14-G1).  At the base of the prominent sandstone, you can see some rip-up clasts, torn by the high-energy river from the underlying siltstone, which was itself deposited in the river's floodplain. Within the sandstone, you can also see cross-bedding, which indicates the direction the water flowed when depositing the sand (Figures 14-G2 and 14-G3).

39.4 – Pass through a slightly open area with lake views, R. These will continue for a short distance.

14-H:  Here you encounter another diabase dike.  This one trends about N10°W and can be traced through the woods.

39.5 – The trail starts to head “inland”.

39.6 – Within view of a graveled road, L, the Falls Lake Trail turns R as it starts to parallel the road. Soon cross the opening of a drainage pipe and eventually make a second R to leave the road.

39.8 – Possible lake views, R.

40.1 – Cross a roadbed, coming from a residence. Soon start to walk by the lakeshore, R.

14-I:  You can see several large accumulations of diabase along the lakeshore here.  The northernmost group has several pieces that have a hexagonal shape.  This shape is due to columnar jointing, a feature that resulted from the rapid cooling of the diabase magma.  The hexagonal columns originally form perpendicular to the surface against which the magma cooled.

What is the nature of the diabase here?  There are three possibilities:  (1) the piles could all be part of one large steeply dipping dike that parallels the lakeshore, about N30°E; (2) each pile may represent a separate steeply dipping dike trending NW; or (3) they may all belong to a sill - a nearly flat-lying body that was intruded parallel to and between the sedimentary beds above and below it.  What do you think?  How would you test these theories?

40.2 – Cross a path from a residence, L.

14-J:  There is a large block of diabase here behind a house.

40.5 – Cross an overgrown roadbed and soon a possibly, dry Creek bed.

14-K:  More diabase.

40.6 – Reach another old roadbed. Cross it and veer towards R to stay on the trail.

14-L:  More diabase.

40.7 – Pass some trail signage and veer to the L by a residence. Soon start to walk near, but above, the lake shore.

14-M:  Still more diabase.

40.9 – Reach a gravel road (private) as the trail turns R to follow it.

41.0 – After the road goes over the dam of a small pond, L, turn R to reenter the woods.

14-N:  Even more diabase.  All this diabase suggests that we are probably walking through a sill.  If it were a dike, or several dikes, they would all fall in lines.

41.2 – The trail crosses a narrow path.

41.3 – Cross another roadbed, with a blue-blazed connection (0.1 mi L) to Santee Road.

14-O:  More diabase as you approach Santee Road.

41.5 – Cross under a powerline.

41.7 mi – Reach another powerline. The lake is R.   To continue to Section 15, cross over Little Lick Creek using the new trail bridge.

End of Trail Section 14

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