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Coastal & Marine Geology Program > Center for Coastal & Regional Marine Studies > Geologic Characterization of Lakes and Rivers of Northeast Florida > OFR 00-180

Subsurface Characterization of Selected Water Bodies in the St Johns River Water Management District, Northeast Florida

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Lake Johnson
Clay County, Florida

Introduction | Subsurface Characterization


Lake Johnson Seismic Track Map.
Seismic Survey Track Map. Click on the image to see a larger version.

Lake Johnson lies within the Central Lake District physiographic province. It is within the Interlachen Sand Hills subdistrict (see Fig. 7, Regional Geology). The lake is adjacent to the Trail Ridge Sands which is a paleodune ridge that extends north into Georgia. This region includes the largest number of cover collapse sinkholes and provides direct recharge to the underlying Floridan aquifer system. Vegetation that includes longleaf pine and turkey oak is prevalent. Internal drainage through the sinkhole lakes has limited the formation of streams except during periods of high rainfall.

The surficial sands provide storage for rainfall and recharge to the lakes during high water-table conditions. The potentiometric surface of the Floridan aquifer is lower than the lake so a continual downward gradient exists and provides the mechanism for recharge. Pathways for recharge exist where the thick clay and sandy clay units within the Hawthorn Group are breached by collapse sinkholes.

The unique physiography of the region can be seen in the hillshade view presented on Index Map A. The landscape is dotted with lakes that are incised into the surrounding sand hills. Large, flat bottom prairies, such as Levys Prairie in the southwest section of the Interlachen Sand Hills, attest to the erosional process of internal drainage into sinkholes. There is only a poorly developed surface water drainage system in the sand hills. A well developed drainage can be seen in the northeast section of Index Map A in the Penny Farms Uplands. This is related to the thicker section of Hawthorn Group and the lack of sinkhole development.

The irregular shape of Lake Johnson gives it a perimeter of over 10 km, with an area of only 2 km2 (see Track Map). Lake level at the time of the survey was 29 m (95 ft) NGVD. Gold Head Branch flows into Lake Johnson from the northwest and there is no surface water outflow points.

Coastal & Marine Geology Program > Center for Coastal & Regional Marine Studies > Geologic Characterization of Lakes and Rivers of Northeast Florida > OFR 00-180 U. S. Department of the Interior | U.S. Geological Survey
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Updated May 06, 2013 @ 09:24 AM (JSS)