General

Except for a downfaulted block of Hickory Sandstone (Cambrian) within the road trip and the Hunneycut and Gorman formations of the Ellenburger Group at the south-southwest end of the route, the rocks are preCambrian Packsaddle Schist and Spring Valley Gneiss with a few exposures of granite. Just east of the turnoff to Horseshoe Bay, a fault separates preCambrian and Ordivician rocks.

Packsaddle Schist metasediments are exposed in a road cut on the northeast side of highway 71 northwest of the Honey Creek bridge. These thinly interlayed gray, tan, black and light brown graphitic and quartzose phyllites, biotite schist and fine-grained quartzites are the metasedimentary package of rocks that marks the base of the Packsaddle Domain. The age is uncertain, but metavolcanic rocks that are interlayered with this sequence at another site crystallized about 1245 million years ago.

A virtual field trip of the Packsaddle Schist at Honey Creek is available from the Lafayette Geological Society.

There is a well-developed south-dipping cleavage in the outcrop. Although the outcrop looks little deformed, tight to isoclinal folds of the phyllites show highly repeated folding episodes.

A small granitic pegmatite intrudes across and distorts the cleavage of the graphitic phyllite. Granite plutonism was after the cleavage formation. A thin bleached zone at the margins of the pegmatite indicates volatilization of graphite during intrusion.

Gold Again!

Back around the turn of the century a newspaper article was published in San Antonio which was typical of the many legends of lost mines in the area of Llano and San Saba Counties. According to the article D.F. Brooks, "says he has discovered on Riley Mountain, west of the Packsaddle group in Llano County, an old Mexican or Mormon gold mine, and the remains of an old smelter a half mile west of Honey Creek and three miles west of the Packsaddle Mountains. The ledge, he says, is a true fissure, forty-five or fifty feet deep. The mine has a six-foot entrance, and both the foot and hanging walls are "pockety". In the center an eighteen-inch pay streak of decomposed sugar quartz is yellow as gold itself.

































The Hickory Sandstone (Cambrian) is deep red, because of abundant hematite. The sand grains are coarse and well rounded. sand-size grains of hematitic ooids resulted from mineral precipitation on fragments moving about in agitated waters of the tidal zone. Tidal conditions are also indicated by cross-bedding, formed as sediment moved by water currents accumulated on a rippled bottom. Fossils of the inarticulate brachiopod Lingula are in hash zones within the sandstone. Trace fossil burrows are on the bases of some of the sandstone layers.

The Hickory Creek Sandstone near Honey Creek is a fault bounded block surrounded by the Precambrian Town Mountain Granite and Valley Spring Gneiss. Small normal faults are exposed along the outcrop in the road cut. These faults offset the strata in the Hickory Sandstone from just a few centimeters to more than several meters. The offset along the faults is clearly visible in several cases by an obvious color change. - photo

Road Log















































legend for the map

mile 0.0 - 31.8 (30o 45.590; 98o 40.510) - Junction of 29, 16, 71

mile 1.4 - 30.4 (30o 44.285; 98o 40.593) - highway 71 departs to left (east-southeast)

mile 2.7 - 29.1 (30o 43.947; 98o 39.420) - preCambrian Spring Valley Gneiss outcrop on right side of highway. Small granite dikes are common at this location.

mile 4.1 - 27.7 (30o 43.083; 98o 38.277) - Spring Valley Gneiss outcrop on left

mile 4.6 - 27.2 (30o 42.894; 98o 37.842) - preCambrian Honey Fm. outcrop of bedded rock on left side.

mile 5.4 - 26.4 (30o 42.715; 98o 36.641) - preCambrian Honey Fm. outcrop left side.

mile 6.5 - 25.3 (30o 42.518; 98o 36.000) - outcrop of Hickory Sandstone member of the Riley Formation (Middle Cambrian) on left; bedded sandstone.

mile 8.1 - 23.7 (30o 42.303; 98o 34.633) - outcrop of the Hickory Sandstone on left.

mile 8.3 - 23.5 (30o 42.249; 98o 34.256) - highway 306 intersection

mile 8.8 - 23.0 (30o 41.925; 98o 34.027) - outcrop of Spring Valley Gneiss (preCambrian) on right. This outcrop is also shown in a closeup view.

mile 9.9 - 21.9 (30o 41.144; 98o 33.596) - highway 307 to Kingsland low-water crossing of the Llano River (see log under Shorter Highway Excursions)

mile 10.0 - 21.8 (30o 41.135; 98o 33.594) - Hickory Sandstone on left.

mile 10.3 - 21.5 (30o 40.713; 98o 33.474) - outcrop both sides, bedded Hickory sandstone. Thinner bedding is seen in the closeup view.

mile 14.1 - 17.7 (30o 37.786; 98o 31.733) - Honey Creek, Packsaddle Schist metasediments near base of the Packsaddle; road cut on NE side of highway immediately NW of Honey Creek bridge.

A virtual field trip of this location can be seen at the 2005 Field Trip, Lafayette Geological Society page.

mile 14.2 - 17.6 (30o 37.777; 98o 31.725) - Honey Creek Bridge

mile 14.9 - 16.9 (30o 37.293; 98o 31.474) - basal Cambrian Hickory Member of the Riley Formation is exposed in the ridge to the left. The Hickory is coarse to medium grained arkose and quartz arenite. contact between Hickory Sandstone and Packsaddle Schist is approximately at the break in slope.

mile 15.8 - 16.0 (30o 36.676; 98o 31.100) - historical marker on left; view northeast of Riley Formation in the Packsaddle Mountain.

mile 16.5 - 15.3 (30o 36.052; 98o 30.704) - marbles of the basal Packsaddle Domain are locally exposed.























legend for the map

mile (19.1) - 12.7 (30o 34.139; 98o 29.130) - highway 2233 to Kingsland

mile 20.1 - 11.7 (30o 33.700; 98o 28.650) - outcrops left and right; bedded schist (preCambrian Honey Fm.) with marble veins across bedding.

mile 20.2 - 11.6 (30o 33.493; 98o 28.381) - Sandy Creek. The sands are derived from the metamorphic rocks.

mile 22.3 - 9.5 (30o ; 98o ) - outcrop (preC Sandy - Packsaddle) on left

mile 22.4 - 9.4 (30o 32.207; 98o 26.584) - highway 962 on right to Round Mountain

mile 22.5 - 9.3 (30o 32.347; 98o 26.773) - outcrop (preC Sandy - Packsaddle) on left.

mile 22.7 - 9.1 (30o 32.103; 98o 26.456) - outcrop (preC Sandy - Packsaddle) on left.

mile 24.5 - 7.3 (30o 31.280; 98o 24.795) - outcrop of Packsaddle Schist on left.

mile 24.7 - 7.1 (30o 31.180; 98o 24.591) - highway to Horseshoe Bay.

mile 25.2 - 6.6 (30o 31.007; 98o 24.130) - Roadcut exposes Packsaddle Schist metasediments and metavolcanics in the lower Packsaddle. The schist is cut with igneous intrusions.

The Marble Falls Fault places down-faulted Gorman Fm. against the preCambrian Packsaddle Schist (to the northeast. At Marble Falls, this fault has 3,000 feet of displacement.

mile 25.3 - 6.5 (30o 30.997; 98o 24.174) - Slick Rock Creek bridge. Fault brecciated Gorman Fm. dolostone is exposed in the stream channel ; probably related to Marble Falls fault.

mile 25.5 - 6.3 (30o 30.939; 98o 23.930) - roadcuts right & left, limestone.

mile 26.4 - 5.4 (30o 30.811; 98o 23.040) - the Honeycut Fm. (Ordovician) has paleokarst features including large-scale solution conduits and terra rossa residual soils.

mile 27.5 - 4.3(30o 30.817; 98o 22.035) - roadside park on left. exposure of medium bedded Gorman Fm. on right side, inside fence.

mile 28.0 - 3.8(30o 30.922; 98o 21.531) - outcrop (Honeycut Fm) on left, limestone.

mile 28.8 - 3.0 (30o 31.040; 98o 20.745) - road cut (Honeycut Fm) right & left, limestone.

mile 29.9 - 1.9 (30o 30.916; 98o 19.565) - outcrop (Honeycut Fm) on left, white limestone; but the outcrop on the right side of the highway is different

mile 30.9 - 0.9 (30o 30.759; 98o 18.572) - outcrops of Ordovician Gorman Formation (of the Ellenburger Group) on both sides of road. The Gorman Fm. is a cherty interbedded limestone and dolomite overlying the Honeycut Fm.

mile 31.8 - 0.0(30o 30.551; 98o 17.763) - intersection with U.S. 281; turn left (north) for Marble Falls

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