Digging Into Foundation

Unfolding underlying layers: Geologist Ice digs into Bosque County’s unique geology at Cranfills Gap Chamber of Commerce meeting as history lays foundation for the future

CRANFILLS GAP – The most important thing in finding a new home, is undoubtedly the location; whether it’s in a preferred school district or neighborhood, proximity to a certain city and amenities, travel time to family, work or church.

Back in 2015, Geoff Ice and his wife Marie chose their home near Cranfills Gap with a unique perspective. A certified petroleum geologist with the American Association of Petroleum Geologists and state-licensed, with over 42 years of experience in petroleum geology, Ice took the land’s underlying layers into consideration. Geologists study the materials, processes, and history of the Earth. They investigate how rocks were formed and what has happened to them since their formation.

Knowing how land is shaped over millions of years, Ice dug deeper than the surface infrastructure to find the land they wanted to build on. He used this unique journey “Why We Came To Cranfills Gap” as a vehicle to explain Bosque County’s unique geology to a large group of people attending the Cranfills Gap Chamber of Commerce monthly meeting May 10.

A Fort Worth resident at the time, Ice immensely enjoyed hunting dove with a friend in Acton and he wanted a sunflower patch of his own to allow for hunting dove close to home.

Researching the Acton sunflower field’s underlying geology, Ice found it was located a northern extension of the Fredricksburg formation created in the early Cretaceous period. So, armed with a road map superimposed on a surface geologic map, the couple went in search of land with similar geological properties. They found that Bosque County and neighboring Hamilton County have an abundance of Walnut Clay, surrounded by Comanche Peak limestone hills. It’s the heavy black soil in Walnut Clay valleys which easily holds sunflower seeds throughout the winter, allowing for another sea of yellow blooms the next fall.

In geology, physiographic regions separate the Earth into different areas based on the predominant types of landforms found in each region. Ice showed that physio graphically Bosque County lies on the Lampasas Cut Plain – an ancient landscape within Central Texas. It is an area of the Edwards Plateau, nestled between the Central Texas Uplift to the west and the Blackland Prairies strip to the east.

Ice went on to explain the different topography layers in the county due to erosional stages in the rock formations.

The Edwards Limestone forms the caprock for the mesas, and there you can find a lot of flint arrow heads. Ice had a large piece of Edwards Limestone with him to illustrate the extreme porous nature of the rock. The Comanche Peak, Walnut and Paluxy formations form the slopes and wide valleys. The deeper laying Glen Rose Limestone which holds the area’s dinosaur tracks is only exposed in deeply entrenched major trunk drainage. The Comanche Peak is more clay rich and holds most fossils.

Springs between the Edwards and Comanche Peak layers wore away the softer limestone, creating the distinct limestone overhangs, like the ones at the Meridian State Park. Native Americans used these overhangs as refuges. The recognizable limestone benches in the Walnut Clay are abundantly seen along Bosque County creeks and river beds. They often contain gastropods, mollusks and oysters. These limestone beds are an excellent natural seal for stock tanks.

Ice wanted all these layers on his property. Initially, Ice’s run-off and seepage-fed stock tank leaked. He explained that he apparently had not dug it deep enough to utilize the deeper laying Walnut limestone bench as its bottom.

With the information presented, the audience was sure to look at their oh-so-familiar Bosque County countryside with more educated eyes, discerning the different layers in the landscape and how they were formed, knowing now where to look for fossils.

With a lot of interest from the audience – some with a more than average knowledge of geology and engineering – Ice would have loved to explain the workings of the Trinity Aquifer, but according to his wife Marie that would be an interesting presentation for another time.

For those wanting to read more about the Lampasas Cut Plain geology, Ice mentioned a 1995 Baylor study by Bradley Clark Parish at https://www.baylor.edu/geosciences/doc.php/287373.pdf


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