Guidebook—Geology of South-central Kansas
Map of field trip route, showing major roads and stops 1 through 4.
This field trip focuses on the rocks and fossils of south-central Kansas, specifically those that crop out in several locations in Greenwood, Woodson, and Wilson counties. Most of the rocks we will see on this trip were deposited during the Pennsylvanian Period of geologic time, about 300 million years ago. We will be in the Osage Cuestas physiographic region for all but one of our stops, which will feature the sandstones common in the Chautauqua Hills region of the state.
This field trip is part of the Kansas Geological Survey's participation in Earth Science Week (October 7-13, 2001), a national celebration of the earth sciences, established in 1998 by the American Geophysical Institute, based in Alexandria, Virginia. Earth Science Week is a time to increase public awareness and understanding of the earth sciences. For more information about Earth Science Week, visit their web site at www.earthsciweek.org.
From El Dorado to Stop 1
We begin our field trip in El Dorado in East Park, just south of the Kansas Oil Museum, which is operated by the Butler County Historical Society. East Park is just west of the Walnut River, and it was the Walnut River valley that inspired an early settler to exclaim "El Dorado!" when he saw the area. El Dorado is Spanish for "land of gold" and was the legendary quest of many early explorers in the New World.
It wasn't until many years later that this region in fact did become the land of gold--black gold. In 1915 oil was discovered about 3 miles northwest of El Dorado on the Stapleton lease in two sandstones 590 and 670 feet below the surface. The El Dorado field was born.
However, the story begins about three years earlier when Erasmus Haworth, an early director of the Kansas Geological Survey, and his son did detailed mapping of the surface rocks in the area around El Dorado. Oil and gas had previously been discovered in the Augusta area in association with what geologists call an anticline, an upward bulge in the earth's strata. Haworth discovered a large anticline near El Dorado and recommended it as a site for oil exploration. On October 6, 1915, Haworth's prediction became a reality when a well belonging to Cities Service struck oil. This was the first discovery of a major oil field using scientific methods, namely detailed geologic mapping of the surface rocks.
In a short time, El Dorado became the largest oil field in Kansas, a distinction it held until just a few years ago. By 1918 oil from the El Dorado field accounted for 12.8% of the nation's production and 9% of the world's production. This field helped fuel our entry into World War I and thus was a factor in the Allied victory.
From East Park we travel east along U.S. Highway 54 (Central Ave), crossing the Walnut River. The elevation here is about 1,260 feet above sea level. As we continue east we will slowly gain elevation as we climb the gentle western slope of the escarpment formed on the limestones of the Barneston Formation. Like most of the rocks in eastern Kansas, the Barneston dips very slightly to the west. It also caps the highest ridges of the Flint Hills, the physiographic region in which El Dorado and most of Butler County lie. However, it is not until we reach the edge of the Barneston escarpment that the scenery takes on the rugged appearance we associate with the Flint Hills.
Flint Hills at dusk, Butler County.
For the first 12 miles of the route, until we get close to the small town of Rosalia, the limestone outcrops will be the uppermost member of the Barneston Formation, the Fort Riley Limestone Member. The Fort Riley is an important limestone resource and there are several quarries in the El Dorado area where it is quarried for aggregate and rip-rap. The Fort Riley has also been used as a building stone; part of the state capitol in Topeka is built from Fort Riley limestone quarried near Junction City. In Cowley County, to the south, the Fort Riley is known locally as Silverdale limestone because of large quarries near the small town of that name.
From Rosalia, we continue eastward over an area in which the Florence Limestone Member is at the surface. The Florence is the lowermost unit in the Barneston and is one of the limestones that contains large amounts of the chert, or flint, that gives this region its name. Chert is chemically similar to quartz, but lacks quartz's crystalline properties and has water as part of its chemical make-up. Flint Hills chert is usually white, gray, pale blue, or brown. Because chert is more resistant to weathering than the surrounding limestone, it remains after the limestone has been worn or dissolved away and litters much of the countryside where it crops out.
Near mile marker 269, U.S. Highway 54 crosses the crest of the Flint Hills escarpment; the elevation here is 1,610 feet, 350 feet above the Walnut River in El Dorado. To the south, the gentle western dip of the rocks is reflected in the dipping horizon formed by the hills.
As we continue east on Highway 54, we cross into Greenwood County and leave the Flint Hills behind, entering the physiographic region called the Osage Cuestas, characterized by limestones and shales that form small, eastward-facing escarpments, or cuestas. When we crossed into Greenwood County, we also crossed a time boundary, leaving behind rocks formed during the Permian Period (less than 290 million years ago) and entering a region where the surface rocks were formed during the Pennsylvanian Period (more than 290 million years ago). Because the deposition of alternating limestones and shales was almost continuous in this area 290 million years ago, geologists debate just where to put the boundary between the two periods. In fact, this boundary has been moved a number of times.
At about mile marker 281, the highway drops off a small escarpment formed on the Bern Limestone (see stratigraphic column below). We will see this formation exposed at Stop 1.
Stratigraphic classification of Upper Pennsylvanian rocks in Kansas (from Zeller, 1968).
As the route continues through Eureka, it crosses Fall River, where the elevation is 1,010 feet, or 250 feet below the Walnut River in El Dorado and 600 feet below the crest of the Flint Hills in Butler County. Eureka is the county seat of Greenwood County.
In Eureka, turn left (north) on Main street and go 1 mile to 13th Street, passing the Greenwood County courthouse. Turn left (north). Continue north 4.5 miles to the entrance of a park-like area near the north end of the dam at Eureka City Lake. We will park here and walk a short distance south to the spillway (Stop 1).
This guidebook is also available in print form as Kansas Geological Survey, Open-file Report 2001-41, from KGS Publications Sales office, 785-864-3965.
Unless noted otherwise, illustrations by Jennifer Sims, Kansas Geological Survey; photographs by John Charlton, Kansas Geological Survey. Text by Jim McCauley, Liz Brosius, Rex Buchanan, and Bob Sawin, Kansas Geological Survey.
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