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Changes to Texas Land
Earth and Space
Changes to Texas Land
Part I: Ecoregions of Texas
Ecoregions
The term ecoregions was developed by combining the terms
“ecology” and “region.” Ecology is the study of the
interrelationship of organisms and their environments. The term,
ecoregions, links ecology to a specific location or region of the
country. Ecoregions are identified by a combination of biotic and
abiotic factors that include: geology, landforms, vegetation,
climate, soils, land use, wildlife, and availability of water.
Texas Ecoregions
Due to its size (266,807 sq. miles) and its geographic location, Texas has more distinct ecoregions
than any other state. Texas has impressive topographic diversity, including 91 mountain peaks that
are a mile or more high. The natural regions of Texas look different from one another, both in terms
of the biotic characteristics (plant and animal communities) and the abiotic characteristics
(topography, geology, soils, and climate).
Texas can be divided into the following 10 natural regions:
Piney Woods
Post Oak Woods and Prairies
Blackland Prairies
South Texas Plains
Gulf Coast Prairies and Marshes
Edwards Plateau
Llano Uplift
Rolling Plains
High Plains
Mountains and Basins
Piney Woods: Located in the eastern portion of the state, the Piney Woods region is a forested
area with a variety of trees and soil types. While pine forests dominate the region many hardwoods
are native to the area as well. The Piney Woods region is the wettest region of Texas with an
average annual rainfall of 32 to 50 inches.
Post Oak Woods and Prairies: Located due west of the Piney Woods and Gulf Coastal Plains
regions, the Post Oak Woods, and Prairies is a region of grasslands with forested areas in the
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Part I: Ecoregions of Texas, continued
bottomlands. The soil type ranges from clay loam to clay in the bottomlands with sand loam or
sandy soil in the upland prairies. This region receives an average annual rainfall of 35 to 45
inches. Cattle ranching and hay production are common in this region.
Blackland Prairies: Located due west of the Post Oak Woods and Prairies, the Blackland Prairies
region is named for its rich, black, heavy, clay soil. The region has gently rolling hills and areas of
level land. In this primarily grass covered region, wooded areas are only found in drainage areas
and along the region’s waterways. This region receives an average annual rainfall of 35 to 45
inches.
South Texas Plains: Located in the southern tip of the state, the South Texas Plains are flat with
some gentle rolling hills. The region is dry receiving only an average annual rainfall of 19 to 23
inches. The acidic sandy soil supports shrubs and small trees, mainly mesquite, and huisache. A
few major rivers flow through this region.
Gulf Coast Prairies and Marshes: Located along the Gulf of Mexico, the Gulf Coast Prairies and
Marshes are flat lands that are good for agriculture. The sandy soils support mesquite trees and
farm crops such as cotton, sorghum, wheat, and corn. The region also supports cattle grazing.
Mudflats and saltwater marshes are found close to the shoreline. The area receives an average
annual rainfall of 23 to 56 inches.
Edwards Plateau: Located in the south central portion of the state at the point of the “big bend” in
the Rio Grande river, the Edwards Plateau varies in elevation from 600 feet in the east to over
3000 feet to the south and west of the region. The soils vary from a shallow layer of mottled yellow
clay to clay loam which quickly becomes rocky clay or solid limestone as you dig beneath the
surface. The region supports grasses of varying heights and hardwood forests. Fruit and vegetable
crops are commonly grown in the region. The area has an average annual rainfall of 23 to 35
inches.
Llano Uplift: Located in the center of the state, this region is known for its unique minerals and rock
formations of large granite domes. The elevation of the area varies from 825 feet to 2250 feet
creating a hilly terrain. The coarse sandy soils support hardwoods, shrubs, and grasslands. Cattle
ranching is common in this region. The area receives an average annual rainfall of 24 to 32 inches.
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Part I: Ecoregions of Texas, continued
Rolling Plains: Located in the northern section of the state just east of the High Plains region, the
Rolling Plains region is fertile grassland with rough terrain. The elevation varies from 1000 to 3000
feet. The neutral to alkaline soils support a variety of vegetation from hardwoods to shrubs to
grasses. Economic pursuits in this region include oil and gas production, cattle ranching, cotton,
sorghum, and game hunting. The area receives an average annual rainfall of 22 to 30 inches.
High Plains: Located in the panhandle, this region is part of the largest and most completely flat
areas of the world. The soil is alkaline, heavy clay which supports the growth of short grasses and
shrub trees like mesquite. The area receives an average annual rainfall of 23 to 35 inches. Drilling
for oil and gas is the main economic pursuit in this region.
Mountains and Basins: Located in far west Texas, this region ranges in elevation from 5000 to over
8700 feet. The highest mountain in the region, and in the state, is Guadalupe Peak, which reaches
8749 feet. Pine forests grow in the higher elevations with juniper and oak trees growing in the
canyons. The area receives an average annual rainfall of 12 to 20 inches with a greater amount
falling in the higher elevations.
Procedure
1.  Use Map #1, “Ecoregions of Texas” as a guide to shade in the Ecoregions Map in your Student
Journal. Create a color key and legend.
2.  Use the background information and the maps to analyze the abiotic and biotic factors that
make each ecoregion distinctive. Record this information in the middle column of the
Ecoregions in Texas data table in your Student Journal.
3.  Use the Photo Gallery and examine the photos #1-4 in the Collage of Texas Landscapes.
Discuss the details of the photos with your lab group.
4.  Match each of the photos to a specific ecoregion and explain why you think the picture is a
good match for a particular ecoregion in the third column of the data table titled: Ecoregions in
Texas in your Student Journal. There are only four photo examples for all of the ecoregions
listed, so choose four that best fit the four photos.
Complete Part I in your Student Journal.
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Changes to Texas Land
Earth and Space
Part II: Weathering Models
Weathering
Weathering is the term used to describe the group of destructive forces that change the
physical and chemical character of rock near Earth’s surface. Weathering can occur on the surface
of the rock while it lies still in the ground. Weathering also occurs as an on-going process while
rock material is carried in streams or blown in the wind during erosion. There are two general types
of weathering: mechanical and chemical. Both mechanical and chemical weathering cause the
destruction of earth materials.
Mechanical weathering (or physical breakdown) is the breaking down of rocks into smaller
pieces. The change in the rock is physical with no chemical change. This is similar to what
happens if you break a glass bottle. The broken chunks of glass are smaller than the original whole
structure, but each chunk of glass still has the same chemistry and properties. Agents (causes) of
mechanical weathering include: wind, ice, moving water, temperature changes, and plant and
animal activity.
Water is a powerful weathering agent. The “freeze- thaw” process of ice wedging occurs when
water freezes after entering a crack or fracture in a rock, the water expands and forces a larger
opening in the rock. Over time, this process can break large rocks into small pebbles. Wind can
also cause significant weathering on rock surfaces. Strong winds carrying fine sand particles can
act like a sand-blasting machine, attacking the face of a cliff or the surface of a rock on the ground.
Perhaps the greatest amount of mechanical weathering is done in streams and rivers where rock
fragments are rolled around and crashed into each other, breaking off rock edges, and rounding
the rock particle’s surface.
Chemical weathering is the slow decomposition of rock from exposure to water and atmospheric
gases over time. Carbon dioxide, oxygen, and water vapor are common chemical weathering
agents. As rock is decomposed by these agents, new chemical compounds form. In some cases, a
portion or all of the elements in the rock breakdown into small bits and are washed or blown away.
Different chemical reactions occur, depending upon the chemical composition of the exposed rock
surface.
Please continue with Part II on the following page.
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Changes to Texas Land
Earth and Space
Part II: Weathering Models
The shaping of landforms begins with the weathering process. You will
investigate the two types of weathering, or the gradual wearing down of
a geological formation due to physical or chemical changes to the
surface of rocks.
Mechanical Weathering
1.  Use the nail to carefully puncture a small 3 mm sized hole in the
bottom of cups 1 and 2.
2.  Roll up a paper towel into a narrow strip. Wrap it around the upper
part of cup 1. Tape the towel into place. Roll up a second paper
towel into a narrow strip, wrap it around cup 2 and tape into place.
Set cup 2 into cup 3 (as pictured).
3.  Pour all the salt into cup 2. Draw a “before” diagram of the salt in your Student Journal.
4.  Place cup 1 into cup 2 so that the cups are stacked with one on the top and three on the
bottom.
5.  Slowly pour the water into cup 1.
6.  Monitor the water collecting in the base of cup 3. Stop pouring water before the surface of the
collecting water reaches the bottom of cup 2.
7.  Observe the changes in the salt and draw an “after” diagram in your Student Journal.
Complete the mechanical weathering portion of Part II in your Student Journal.
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Part II: Weathering Models, continued
Chemical Weathering:
1.  Place a small sample of limestone in a Petri dish.
2.  Place 5 mL of acetic acid (vinegar) on the limestone using a dropper.
3.  Records your observations in your Student Journal.
4.  Remove the sample of limestone from the petri dish and observe the matter remaining in the
dish.
5.  Record your observations in your Student Journal.
Part III: Mix and Match–Pick It Up or Drop It Off
Erosion occurs when the rock or soil of Earth’s surface is moved to another location by the flow of
water, ice, or wind as well as the constant pull of gravity. The three most common erosion agents
are wind, running water, and ice.
Erosion by Wind
When considering the erosional work done by wind, it is important to think of the process of sandblasting. The moving air picks up small rock particles and flings them at other surfaces. A strong
wind can sand-blast the paint off the side of a house, as well as tear the shingles off of the roof.
Wind action is much more effective in arid areas where there is little vegetation to hold the soil and
fine rock fragments in place. Even fine sediments can act like a sand-blasting machine, abrading
the surfaces of rocks, automobiles, and buildings. Animals and people caught in dust storms risk
inhaling the fine rock particles.
Erosion by Running Water
Moving water is a powerful erosional agent. During flood stage, rivers can move massive amounts
of sediment. Even the rainwater flowing across a lawn is able to pick up and transport soil particles.
Running water is the most common agent of erosion. This includes rain flowing on the hillsides as
well as water in the rivers. Rivers do not have to be in flood stage to erode, however, greater
velocity and volume of moving water result in higher rates of erosion.
Complete Part II of your Student Journal.
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Part III: Mix and Match–Pick It Up or Drop It Off, continued
Erosion by Ice
Glaciers are the primary example of ice as an erosional agent. There are two types of glaciers:
alpine (in mountainous regions) and continental. Alpine glaciers carve out the majestic, rugged,
mountain valleys. Continental glaciers are massive blankets of ice covering thousands of square
miles. A modern example of a continental glacier is in Antarctica. Both alpine and continental
glaciers work as powerful erosional bulldozers, moving massive amounts of rock materials.
Glaciers can gouge out portions of rocks to create landforms like the Great Lakes. Evidence of the
power of glaciers can be studied in the glaciers of today and in the sediments left in previously
glaciated regions of the world.
Deposition occurs as sediment, created by weathering and moved by erosion, settles in a different
location due to gravity. Not only is gravity the driving force that causes weathered boulders to fall
off the face of a cliff, but it is also the force the keeps glaciers and rivers moving to lower and lower
elevations. Deposition is a constructive process that builds up earth materials in layers.
Wind Deposition
Fine sands blown in the wind are sometimes deposited as sand dunes. (Not all material carried by
wind ends up in a dune!) Dunes form as rounded sand grains built up in a pile. Because layer after
layer of sand is rolled up the windward side of the dune and then falls to the protected leeward (or
slip face) side, dunes develop a distinct layered structure.
Ice Deposition
Because glaciers erode primarily by plucking up rocks of all sizes and then pushing piles of rock
across the land, the deposits left by glaciers are often found as elongated mounds marking the end
or sides of the sheet of ice when they melted away. These mounds of loose rock are referred to as
moraines and are characterized by the fact that the rock fragments are angular or sharp-edged,
not rounded like river rocks. Another distinctive characteristic is that rocks of all sizes are mixed
together. Some of these rocks can be very large because thick sheets of ice are very powerful
erosional agents. Parts of North America were covered by a sheet of glacial ice as recently as
10,000 years ago and sediment deposits from that period can be found today.
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Earth and Space
Part III: Mix and Match–Pick It Up or Drop It Off, continued
Water Deposition
Rivers and streams are constantly picking up rocks and fine sediments from their banks and
channel bottoms and moving them down stream. Much of the material is rolled along the bottom
and as a result, the sharp edges are broken off, leaving rounded pebbles and boulders. When the
running water slows, it drops sediments in places like in the bend of a river or on sandbars.
Procedure:
1.  Look at the images found in the Student Reference Sheet: Photo Gallery in the Mix and Match
– Pick it Up or Drop it Off section.
2.  There are clues in the background of the images that you will use as evidence to identify the
erosional and depositional processes.
3.  Record your answers on the chart and answer the questions about erosion and deposition in
your Student Journal.
Complete Part III and the Reflections and Conclusions questions in your Student Journal.
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