Article Title

Archeological Survey of Three Bridge Replacements along SH 97 LaSalle and McMullen Counties, Texas.

Authors

Christopher Ringstaff

Agency

Texas Historical Commission

Abstract

On March 12, 2015, TxDOT conducted an intensive archeological survey for the proposed to replacement of three bridges along SH 97 in LaSalle and McMullen Counties. The bridges are located north of the town of Fowlerton, Texas. The first bridge crosses the Frio River, the second crosses a tributary of the Mossy Slough both in LaSalle County. The third bridge crosses the Mossy Slough just past the LaSalle County line in McMullen County. The total area of potential effects (APE) for all three bridge replacements is 8.4 acres. No new ROW or easements are proposed for the project. Although the schematic design plans show only fill being added to the existing ground surface of the roadway approaches, depth of impact for the support pilings is estimated at approximately 50 feet.

A 100 percent pedestrian survey was conducted at all three proposed bridge replacement project areas. The pedestrian survey noted significant ground disturbing impacts from prior bridge construction and utility installation. In particular, extensive fill sections are present to elevate the roadway over the broad floodplain of the Frio River Valley across which all three bridges are located.

Subsequent to the pedestrian survey, backhoe trenching was conducted at the Frio River and Mossy Slough Bridges. The Mossy Slough Tributary Bridge was not trenched based on a combination of factors including modern age, short span, and existing impacts. The observations from both the pedestrian survey and subsurface testing revealed no archeological materials or features. Although trenching at the Frio River Bridge terrace showed a relatively intact soil profile (despite the absence of archeological materials and features), trenching at the Mossy Slough did reveal extensive fill even in the spanned terrace within the APE.

A TxDOT archeologist evaluated the potential for the proposed undertaking to affect archeological historic properties (36 CFR 800.16(l)) or State Antiquities Landmarks (13 TAC 26.12) in the APE for the proposed SH 97 bridge replacements. Based on the combined pedestrian survey of the backhoe trenching, no archeological sites or materials were observed in the proposed project areas. In addition, the majority of the APE had been substantively impacted by prior transportation construction and utilities leaving only small areas of intact alluvium to examine. Based on these observed impacts and the results of the survey, any sites in the APE would likely lack sufficient integrity of location, association, and materials to be able to address important questions of prehistory or history (36CFR60.4 and would not be considered eligible for listing to the NRHP (36 CFR 60.4) or for designation as a SAL (13 TAC 26.8) and no further work is warranted for the project areas.

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