Homestead National Monument of America, Geologic Resources Inventory Report

Authors

J. Graham, United States National Park Service

Date of this Version

9-2011

Citation

Natural Resource Report NPS/NRSS/GRD/NRR 2011/452 / NPS 368/110513, September 2011: vi, 43 pages

Published by the United States Department of the Interior, National Park Service, Natural Resource Stewardship and Science, Fort Collins, Colorado

Also available at: http://www.nature.nps.gov/geology/inventory/gre_publications.cfm

http://www.nature.nps.gov/publications/nrpm/

Please cite this publication as:

Graham, J. 2011. Homestead National Monument of America: geologic resources inventory report. Natural Resource Report NPS/NRSS/GRD/NRR—2011/452. National Park Service, Fort Collins, Colorado.

Comments

United States government work. Public domain material.

Abstract

Executive Summary

This report accompanies the digital geologic map data for Homestead National Monument of America in Nebraska, produced by the Geologic Resources Division in collaboration with its partners. It contains information relevant to resource management and scientific research. This document incorporates preexisting geologic information and does not include new data or additional fieldwork.

Established as a memorial to pioneer life and the Homestead Act of 1862, Homestead National Monument of America preserves approximately 92 ha (228 acres) of terraced grassland and riparian, floodplain environments. Included in the monument are about 40 ha (100 acres) of restored tallgrass prairie and a rare, mesic bur oak (or burr oak) forest community. Cub Creek meanders through the western and northern sections of the monument past the homestead of Daniel Freeman, the first United States citizen to file for land under the Homestead Act of 1862.

Located within the Central Lowland physiographic province, Homestead National Monument of America encompasses a landscape carved by continental glaciation and subsequent erosion. River terraces, floodplain, and alluvial deposits in the monument and surrounding region not only provide clues to the post-ice age geologic history but also contribute archeological resources from both American Indian and Euro-American settlements.

Flooding and bank erosion along Cub Creek and surficial geologic mapping form the primary geologic issues that may affect resource management decisions at Homestead National Monument of America. Minor issues include potential seismic (earthquake) hazards and external activities such as quarrying operations and hydrocarbon exploration.

Flow in Cub Creek is controlled by upstream dams and water control structures. However, a major flood event could cause damage to historic buildings, septic systems in the monument, maintenance facilities, and other infrastructure. Museum collections, archives, and galleries in the monument have been moved to the new Homestead Heritage Center, located outside of the 100-year floodplain. Bank erosion caused by seasonal flooding may increase the sediment load in Cub Creek. Erosion may expose additional archeological sites, but it may also destroy existing sites.

Because bedrock is not exposed in the monument, a surficial geologic map would prove more beneficial to resource management than a bedrock map. Some of the features that could be identified on a surficial map include the specific lithology and age of unconsolidated surface deposits, geomorphic features, sampling sites along Cub Creek, and known and potential archaeological sites.

Although rare in Nebraska, earthquakes have been known to occur. The largest earthquake in Nebraska occurred in 1877 and split the walls of the Lincoln courthouse. In 2010, a 3.0 magnitude earthquake occurred in central Nebraska about 30 km (20 miles) north of Lexington. Seismic data indicate that active stress is still being applied to the Humboldt fault zone, east of Homestead National Monument of America, but also that the potential for significant ground shaking resulting from an earthquake in the area remains extremely low.

Quarrying operations and hydrocarbon exploration are also potentially minor, external issues for Homestead National Monument of America. Limestone, sand, and gravel have been quarried for cement, road material, riprap, and other purposes in southeastern Nebraska. A surficial map could identify potential areas where quarrying might occur. Oil is produced in the Forest City Basin, which intersects the southeastern corner of Nebraska approximately 113 km (70 miles) from the monument, but no hydrocarbons have been discovered in the vicinity of Homestead National Monument of America. Increased road traffic from hydrocarbon exploration in southeastern Nebraska may pose a minor external issue for the monument.

The surface geology at Homestead National Monument of America records a relatively young geologic history dating back to the end of the Pleistocene ice ages, about 10,000 to 12,000 years ago. Remnants of glacial and interglacial episodes lie between the surface deposits and the bedrock beneath the monument. Exposed in road cuts and along river banks, Pleistocene sediments include glacial till and interglacial deposits such as loess (windblown silt) and outwash sand.

Processes such as wind and water erosion, transportation, and deposition create and shape a rich variety of depositional environments. For example, beneath Homestead National Monument of America, coastal plain and estuary deposits form the Cretaceous Dakota Formation (Dakota Sandstone in the digital geologic data). Incursions of shallow seas into Nebraska during the Pennsylvanian and Permian resulted in a variety of marine and terrestrial depositional environments, several of which can be seen in exposures along the Missouri River.

Knowledge of the physical properties of the different geologic units mapped in the subsurface provides an additional interpretive dimension to the story of Homestead National Monument of America. This report includes a Map Unit Properties Table that describes characteristics such as erosion resistance, suitability for infrastructure development, geologic significance, recreation potential, and associated cultural and mineral resources for each mapped geologic unit in the vicinity of the monument. A surficial geologic map would add significant data to this table.

This report also provides a glossary, which contains explanations of technical, geologic terms, including terms on the map unit properties table. Additionally, a geologic timescale shows the chronologic arrangement of major geologic events, with the oldest events and time units at the bottom and the youngest at the top. The timescale is organized using formally accepted geologic-time subdivisions and ages.