Physical Terrain

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Chapter 2

Washington has a diverse natural environment. The Cascade Mountains divide the state into two extremely different natural environments. Those areas west of the Cascades have a mild and moist climate. This moist climate allows dense forests and vegetation to grow.

The areas east of the Cascades, in contrast, have a harsh and dry climate. This dry climate allows mostly short grasses and sagebrush to grow. Drive over the mountain passes and you can very easily see the contrasts between western and eastern Washington. Contrasts are evident throughout the state of Washington. The saltwater environment of our bays, inlets, and harbors is different from the freshwater environment of Washington’s lakes and rivers. Hundreds of small rivers and streams do not compare in size to the Columbia River.

Our land changes quickly from the flat floodplains in the valleys to the tall mountain peaks and volcanoes. Low, rounded hills differ greatly from the towering jagged cliffs of the North Cascades. The huge Columbia Plateau easily dominates the much smaller Waterville Plateau. Hundreds of our small islands do not compare in size to Whidbey Island, the second largest island in the lower 48 states. Numerous peninsulas cannot compare in size to the Olympic Peninsula. All these contrasts in our state make for an amazingly diverse natural environment.

In this chapter, we will focus on physical features and how they affect the natural environment of Washington. Geologists classify landforms into five different categories: mountains, hills, plateaus, plains, and river valleys. Landforms, no matter the type, are constantly eroded by the forces of nature. As was discussed in Chapter One, volcanic activity, glaciation, and erosion have changed and shaped Washington’s physical terrain.
Physical Terrain

The physical terrain in Washington is diverse. There is very little level land and several mountain ranges. Elevations in the state range from sea level to 14,411 feet at Mount Rainier. Mountains, the first landform we will discuss, are obviously the easiest of the five to recognize.


The state of Washington has several mountainous landforms. There are five major mountain groups. The first and largest of the mountain ranges is the Cascades. A smaller group of mountains is the Olympics on the

Olympic Peninsula. The third largest group of mountains, the Rockies, can be found on the eastern border of Washington. The Blue Mountains in southeastern Washington make up the fourth group. The Okanogan Highlands of north central Washington are the final and smallest group. Of these five major groups, only the Olympics are located totally within the state of Washington. The other mountains also rise into neighboring states and Canadian provinces. Of the five groups, the Cascade Mountains have the largest impact on our natural environment.

The Cascade Mountains are the most

significant range in our state. They extend 600

miles south from British Columbia through Washington and Oregon into northern California. Many of the Cascade peaks rise to an elevation of 5,000 to 8,000 feet above sea level.

Several volcanic peaks rise even higher.

Washington’s tallest volcanic peak is Mount Rainier. It has an elevation of 14,411 feet and is the largest volcano in the Cascade Range. Four other volcanoes surround it, two are situated to the north and two to the south. The largest of the southern volcanoes is Mount Adams with an elevation of 12,307 feet. Forty miles west of it is the smallest of our volcanoes, Mount Saint Helens. On May 18, 1980, when Mount St. Helens erupted, it instantly lost 1,312 feet of its peak. The peak of Mount St. Helens now only rises 8,365 feet above sea level.

The scenic volcanic peak of Mount Baker is

100 miles to the north of Mount Rainier. Mount Baker has an elevation of 10,778 feet. The least known volcano in Washington is Glacier Peak. Glacier Peak is a beautiful mountain located just west of Lake Chelan. It stands 10,434 feet above sea level and is the oldest of our volcanic peaks.

The Cascade Mountains are our state’s most

significant barrier. This chain of mountains divides Washington into two natural environments. These regions are western and eastern Washington. As discussed earlier, western Washington has a mild and moist climate compared to eastern Washington. The Cascade Mountains form a physical barrier to moisture blowing in from the Pacific Ocean. This barrier creates a rainshadow effect . The Cascade Mountains also present a physical barrier to travel, especially during the winter season. Travel is difficult over the mountains because of the high elevations and heavy winter snow.

The most frequently traveled mountain passes are Snoqualmie and Stevens. These mountain passes are often closed in winter for avalanche control and snow removal. Several other less traveled mountain passes are closed for most of the winter because snow removal is too difficult.

The towering snow-capped peaks make the

Cascade Mountains a scenic drive any time of the year. Another scenic mountain range in Washington is the Olympics.

The Olympic Mountains form the large peninsula of western Washington. A peninsula is an area of land surrounded by water on three sides. The Pacific Ocean surrounds the Olympic Peninsula to the west. The northern extent of the peninsula is the Strait of Juan de Fuca. Water from the Pacific Ocean fills Hood Canal, which forms the eastern boundary of the Olympic Peninsula. These young and rugged mountains used to be an offshore island much like Vancouver Island is today. Due to plate movement, this island slowly moved south with the Juan de Fuca Plate. Eventually it joined with Washington. As it did, pressure pushed these mountains higher out of the Pacific Ocean. The Olympic Mountains quickly rose to an elevation of nearly 8,000 feet. The beautiful Olympic Mountains are host to

one of our nation’s national parks.

Olympic National Park includes much of the mountain range and ocean beaches along the Pacific Ocean. The Olympics also receive more precipitation than any area within the lower 48 states. This abundance of moisture allows the Olympic Mountains to host the only rain forest in North America. Are you aware of any other rain forests in the world?

The Hoh rain forest, in Washington, is filled with moss-covered 1,000-year-old evergreen trees that tower over 250 feet above the forest floor. In contrast to the lush rain forest are the highest elevations of the Olympic Mountains. These rugged peaks are covered in low vegetation and snow much of the year.
Okanogan Highlands

In northeastern Washington, just north of the Columbia River, are the beautiful Okanogan Highlands. The highlands combine with the San Poil and Selkirk mountains to form a portion of the western Rocky Mountains. The remote Okanogan Highlands were once covered by large lobes of continental glaciers. The glaciers eroded and carved the deep river valleys. Sparse

vegetation and very limited pine forests cover most of this region. However, the vegetation becomes far more dense in the remote Blue Mountains.
Blue Mountains

The Blue Mountains are an offshoot of the Rockies and are located in southeastern Washington. These mountains were formed by the uplifting of the Columbia Plateau. The Blue Mountains were a physical obstacle for those who once traveled west along the Oregon Trail. The high temperatures and dry, rugged landscape made travel by wagon very difficult. The higher elevations of the Blue Mountains are one of the few forested regions in the state’s interior. In contrast, the lower slopes of the mountains are covered in grasses. Before we end our focus on the mountainous areas of Washington, it is good to take note of the diversity of our mountains. There are many important differences from one mountain region to the next. Moving down the slopes of our mountains to the hills, we find that there is great diversity here as well.


Hills are landforms between 500 and 2,000 feet of local relief. Do you remember our discussion about local relief? Wherever mountains exist, the lower slopes are called foothills. The Olympic, Cascade, and Rocky mountains all have foothills. Two of our most important hills are the Willapa and Palouse. The Palouse Hills in southeastern Washington are large, rolling hills. They were formed by wind blown soil, called glacial till, during the ice ages. These hills are now productive farmland. In contrast, the Willapa Hills of southwestern Washington were formed by plate tectonics. These heavily forested hills produce much of the timber in our state. The lower elevations of the Olympic Mountains and Rockies are not nearly as economically important to Washington as the western and eastern foothills of the Cascade Mountains. The Cascade foothills are important for their lumber, minerals, grassland, and beauty.


Perhaps the most difficult physical landform to recognize and define is the plateau. A plateau is usually a tableland with an elevation of over 2,000 feet. A plateau will usually have a steep cliff on at least one side. It is often surrounded by mountains and deeply eroded by a river.

The Columbia Plateau covers much of eastern Washington and Oregon, as well as southern Idaho. The Columbia River eroded a deep valley around the estern edge of the plateau. The steep cliffs expose many layers of basalt to the forces of wind and water. The surface of the Columbia Plateau is also scarred. Glacial floods, dozens of times, released massive amounts of water across the tableland surface of the Columbia Plateau. These scars are known as the Channeled Scablands. Other features left by the glacial floods are falls, plunge

pools, and coulees.

Coastal Plains

The smallest landform in Washington is our coastal plain. A plain is defined as any area with a local relief of less than 500 feet. Much of our plain lies near or along our Pacific coastline, so we refer to it as a coastal plain. Our coastal plain is long and very narrow. The coastal plain varies greatly from one location to the next. The southern coastal areas are gently sloping with wide sandy beaches. In contrast, the northern coastline is rugged with steep cliffs jutting from the ocean. Gravel, rocks, and driftwood cover the narrow beach. This type of coastline offers little protection from the pounding surf.

Within our coastal plain are numerous harbors and bays. Many have deep water. They provide protection from the violent surf and ocean storms. These two factors make our bays and harbors excellent areas for seaports.

Our inland coastal lowlands are different from the Pacific coastal plain. The coastal lowlands are home to numerous bays, harbors, peninsulas, and islands. Like our coastal harbors and bays, the lowlands are also protected. They have deep natural harbors. Some of these major inland waterways include the Strait of Juan de Fuca, Hood Canal, and Puget Sound.

The inland coastal lowlands are covered in dense vegetation. The beaches are usually rocky with an occasional sandy beach. The tides have a much more prominent effect on the beaches of this region. At low tide, marshes and tidal flats are exposed to reveal their bounty of oysters, clams, and other sea life. The inland coastal plain is protected from the direct effect of Pacific storms. Occasionally this region has a severe storm. Its pounding surf can erode the land or beaches.
River Valleys

Ample rain and snow provide our abundant fresh water. Water finds its way into our state’s numerous rivers. Rivers and their valleys vary greatly in length, flow, and source from east to west.

Western Washington river valleys are very short, yet abundant. These rivers only travel a short distance from the higher elevations of our mountains. They flow directly into the ocean or one of our many harbors, bays, or sounds. These rivers tend to flood during the wet season.

Heavy rains in combination with warm temperatures can cause these rivers to flood. The warm temperatures melt the mountain snow. As the water from the melting snow combines with the rain water, these rivers flood. Floods are destructive to personal property, but they are also an important process of nature. The water, rich with minerals, deposits new topsoil onto the floodplain. Some of western Washington’s more prominent river valleys are the Skagit, Cowlitz, Chehalis, and Snoqualmie. All of these rivers are prone to flooding during the winter months.

Eastern Washington has fewer river valleys, but these rivers carry large volumes of water to the Pacific Ocean. The two largest rivers in our state are the Columbia and Snake. Both rivers have carved deep and narrow valleys into the basalt of the Columbia Plateau. These types of river valleys are ideal for the construction of multipurpose dams. Dams produce electricity, store water, and provide the needed irrigation water for the farmland. The dry farmland of eastern Washington needs irrigation water to be productive. The water is pumped from lakes, or reservoirs, behind the dams. The water is then transported by canals to the farmland where it is used to water the crops. Without these rivers and their dams, water would not be available to irrigate the crops. The dry, or arid, land could not produce many of the crops grown today. Without irrigation the desert would reclaim the land from the farmers.
Natural Environment

Washington has a very diverse natural environment. Natural environment includes climate, natural vegetation, and types of soil. Of all the factors, the most important is geographic location. Location affects every aspect of the natural environment. The state of Washington is located almost midway between the equator and the North Pole. The state lies between the Columbia River (46°N Latitude) to the south and the Canadian border (49°N Latitude) to the north. The winds normally blow from the west across the Pacific Ocean onto the North American continent. Washington is located east of the Pacific Ocean. The marine influence affects both our temperature and amount of precipitation.

Generally, landmasses in the middle latitudes located near large water bodies have cooler summers and milder winters. Marine air tends to cool summer temperatures and warm thewinter temperatures. This is possible because marine air tends to heat and cool slowly. In contrast, air over a landmass tends to heat and cool much faster. Therefore, the temperatures are harsher in these interior regions. This is why the western Washington temperatures are much more constant during the year. Eastern Washington, in contrast, has drastic temperature changes throughout the year. This is because of the continental effect on the climate.

Wind also has an effect on the natural environment. The winds provide an abundance of moisture to western Washington. In contrast, eastern Washington is mostly dry and hot. The difference in natural environments is primarily due to the “rainshadow effect.”

The Cascade Mountains are a physical barrier to the moist air blowing in from the Pacific Ocean. This barrier traps a majority of the moist air on one side, leaving the other side dry. This barrier and its effects on the moisture is one of the most important factors affecting our contrasting natural environment. The rainshadow effect changes the climate, vegetation, and even the soil.

Washington has three general types of climate. These climatic types include west coast marine, highland, and semiarid. The west coast marine climate is found west of the Cascades below 3,000 feet in elevation. The highland climate occurs where elevations are greater than 3,000 feet above sea level. Finally, the semiarid climate is found east of the Cascade Mountains and under 3,000 feet of elevation.

West Coast Marine Climate

The west coast marine climate is located in the lowlands of western Washington. This climate is mild with plenty of moisture throughout the year. Precipitation amounts range from 16 to 200 inches a year. Most areas within this climatic region receive 30 to 60 inches. Much of the moisture falls from October to May. Summer temperatures are mild, normally ranging from 65 to 85 degrees. Temperatures may occasionally reach the high 90s. Winter temperatures are mild and range from 35 to 55 degrees. Temperatures below 32 degrees are rare, and subzero readings are even more uncommon. With the mild annual temperatures and abundance of moisture, the west coast marine climate is ideal for people to live and work. Most of Washington’s population lives within this climatic region. In stark contrast, the highland climate has the fewest people.

Highland Climate

The highland climate covers the higher elevations of the Olympic, Cascade, and Rocky mountains. The summers are short and cool. Winters are long, cold, and wet. The highland climate receives large amounts of precipitation from September to June. Most of the precipitation that falls during these months is in the form of either rain or snow. The highest peaks in this region are capped with glaciers and snow. Mount Baker holds the world’s annual snowfall record. It received a total of 1,124 inches of snow between November 1, 1998 and May 12, 1999.

Semiarid Climate

The semiarid climate is the third major climatic type. A semiarid climate is defined as regions of land that receive less than 20 inches of precipitation a year. Precipitation falls in the form of rain and snow during the winter months. Rain is uncommon during the hot summer months. When it does rain, it usually comes in the form of a thunderstorm.

Long and cold winters are normal for much of eastern Washington. Winter temperatures range from below zero to freezing. In contrast, summer temperatures range from 90 degrees or more. Temperatures over 100 degrees are common in many areas of the semiarid climate. The lack of moisture and high heat during the summer months limits the natural vegetation to grass and sagebrush. Trees grow along streambeds and in the mountains.

Every community in Washington has different weather conditions. Weather is the daily conditions of temperature, barometric pressure, wind, humidity, precipitation, and cloud cover. Each community has a different variation of both weather and climate. Weather represents short-term conditions while climate considers a pattern of a region over a longer period.


Temperature is affected by many different conditions. Latitude is an important factor in influencing temperature. The further north from the equator, the less direct sunlight received by the higher latitudes. Location to large bodies of water is another important factor influencing temperature.

The temperature of water changes very slowly. This slow change in temperature affects the air temperature near the water. Another major influence on temperature is elevation. As we learned earlier, elevation also has an affect on temperatures. Generally, higher elevations have lower temperatures than the areas below.

As you rise in elevation, the temperature decreases three to four degrees for every 1,000 feet. This change in temperature based on elevation is the lapse rate. As we can see by the change in vegetation of eastern Washington, mountains also affect precipitation.


Washington usually receives most of its annual precipitation from early October to April. The driest period of the year is from July through September. The heaviest precipitation occurs in western Washington. However, along the western slopes of the Olympic and the Cascade mountains, the total annual rainfall and snowfall amounts are very high. Precipitation amounts

are significantly less on the eastern slopes of the mountains.

Eastern Washington’s lack of moisture limits its vegetation to grasslands. Short, thin steppe grasses and sagebrush cover the dry landscape. Ranchers raise livestock, and farmers plow the land to raise wheat, barley, and other dry land crops. Humans frequently alter the naturallandscape by planting many crops, shrubs, bushes, and trees.

In contrast, western Washington is covered in dense conifer and deciduous forests. Conifer trees are cone-shaped with a straight trunk, needles, and a shallow root system. The most widespread and valued conifers include Douglas fir, Sitka spruce, pine, western hemlock, and western red cedar. Conifers are a softwood tree. Softwood refers to the ease in which the wood can be cut or worked. A deciduous tree is a hardwood tree. Deciduous trees have a circular shape, deep root system, broad leaves, and short trunks.

The type of vegetation growing in an area is largely determined by the soil. Washington has many different types of soil. Erosion of the mountains brings rich silt or topsoil to the lowlands and river floodplains. Soils moved by water from one area to another are called alluvial soils. These fertile soils are deposited in our major river valleys of western Washington. In contrast, the soils of eastern Washington are primarily the result of wind. These soils, likewise, are very productive. In the hot and dry climate of eastern Washington, water quickly evaporates. This leaves minerals at the surface. This is one reason why the soil is productive when water is added. However, where too much moisture is received, the soil is infertile. Infertile soils are created when water carries the minerals deep into the soil. These are leached soils. This prevents plants from reaching the minerals to help them grow.


Washington’s natural environment offers a moderate climate, lush vegetation, and fertile soils. Washington rarely has natural disasters caused by hurricanes, cyclones, typhoons, tornadoes, or blizzards. However, we do have windstorms, flooding, and drought. Fortunately, these climatic events are usually not life threatening. Our climate makes life enjoyable for the people who live, work, and visit our beautiful state.

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