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The Western San Juan Mountains

Their Geology, Ecology, and Human History

By Rob Blair

Publication Year: 1996

The San Juan Skyway winds its way up, over, and through canyons, mesas, plateaus, mountains, plains, and valleys. The sheer variety of landforms makes the Skyway a veritable classroom for the amateur naturalist and historian. The most complete work published on the natural history of southwest Colorado's majestic mountain system, The Western San Juan Mountains: Their Geology, Ecology, and Human History is designed to be used while exploring the scenic 235-mile paved San Juan Skyway, which passes through Durango, Silverton, Ouray, Telluride, Dolores, and Cortez. The Western San Juan Mountains covers the physical environment, the biological communities, the human history, and points of interest represented on milepost signs along the highway. Some of the many topics covered include: how the San Juan Mountains were formed; why the landscape is so rugged and picturesque; why the vegetation changes from the lowlands to the alpine heights; energy and mineral resources of the area; why these mountains intrigued early explorers; factors that influence the unpredictable weather; and the first-known inhabitants. The contributions to this guide include Fort Lewis College geologists, biologists, archaeologists, historians, and other specialists. Together they have amassed more than one hundred years of study based not only on previous work but on their own research. This generously illustrated guidebook is aimed at all those who wish to understand this intricate mountain system in much greater detail than provided by most picture books.

Published by: University Press of Colorado

Title Page

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pp. vii

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pp. ix-x

Our sense of place comes from knowing where we are, where we have been, and where we are going. Knowing a place means exploring all aspects - geography, history, biology - that make it unique and special. The 235-mile highway loop known as the San Juan Skyway passes through the towns of Durango, Silverton...

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pp. xi-xii

The preceding quotation summarizes the dilemma we faced in producing this text. If we wrote about the complex topics in simple terms, much of what we said would be incorrect. But if we wrote them as if communicating with experts, few readers would be able to understand us. Thus, this book is aimed toward a mid-range...

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pp. xiii

All authors and editors of this book volunteered their own time and effort and paid their own expenses. All chapters were reviewed either by fellow authors and editors or by outside experts. Only the outside reviewers will be acknowledged here. Audrey DcLella Benedict read the entire manuscript and made many insightful...

Part I: Physical Enviroment along the San Juan Skyway

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1. Origin of Landscapes

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pp. 3-17

The San Juan Skyway, a 235-mile highway loop in southwestern Colorado, winds its way up, over, and through canyons, mesas, plateaus, mountains, plains, and valleys. The sheer variety of landforms makes the Skyway a veritable classroom for the student of geomorphology. One explanation for the large diversity of...

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2. Paleotectonic History

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pp. 18-37

To unravel the geologic story of southwestern Colorado, one must understand its paleotectonic history. The field of tectonics looks at the processes that deform the earth's crustal rocks on the global scale; paleotectonics examines such processes over the span of geologic time. The geological evolution of a region such as the...

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3. Precambrian Rocks

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pp. 38-43

The highest peaks of the San Juan Mountains make for some impressive scenery east of U.S. Highway 550 between the Needles store and Molas Lake. The rocks of these peaks were formed during the Precambrian Era between 1.8 and 1.3 billion years ago. Precambrian rocks are also exposed in the steep walls of the...

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4. Paleozoic History

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pp. 44-53

Probably the most confusing aspect of studying the geology of any area is trying to fathom the lengths of time involved. Human references to time - days, months, years, even an average life span - arc simply too short. As a result, geologists have evolved a system that uses strange-sounding words for intervals of time. These...

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5. Mesozoic and Early Cenozoic History

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pp. 54-67

The Mesozoic Era lasted from about 245 million to 66 million years ago. It, like the Paleozoic, is divided into shorter intervals called periods. The periods of the Mesozoic are the Triassic, Jurassic, and Cretaceous (see Stratigraphic Chart, p. 2). These periods are not of equal length: the Cretaceous is the longest, about...

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6. Volcanic Rocks

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pp. 68-79

The San Juan volcanic field is part of a much larger volcanic region that was active throughout the Southern Rocky Mountains from about 40 million to 18 million years ago (Fig. 6.1). Most eruptive centers lie within the region bounded by the Rocky Mountains on the east, the Colorado lineament on the north, and the...

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7. Ore Deposits and Minerals

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pp. 80-95

Gold! Silver! The fabulous riches of the San Juans were discovered in the last quarter of the nineteenth century, and hordes of prospectors poured into the area. Every miner had romantic visions of wealth and dreamed of enjoying the success of Leadville's Horace Tabor or Silverton's Stoiber brothers...

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8. Energy Resources

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pp. 96-112

The scenic San Juan Skyway route lies in a relatively energy-poor corridor between two major oil-and gas-producing basins, the Paradox Basin to the west and the San Juan Basin to the south. Prolific oil fields associated with Pennsylvanian-age (300 million years) algal and oolitic carbonate reservoirs of the Paradox Basin...

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9. Weather and Climate

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pp. 113-126

It only takes a day to drive the San Juan Skyway, but on the right day you can catch a whole year's worth of weather. It is not unusual - especially in the spring - to wake up with frost on the ground, drive through snow, hail, a thunderstorm, and 90-degree heat, and finish the day with a rainbow. The main reason for this variety is, of...

Part II: Biological Communities along the San Juan Skyway

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10. Ecological Patterns

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pp. 129-142

A mantle of green vegetation covers the San Juan Mountains and softens the appearance of the rugged slopes and valleys. The plant life also provides homes for myriad creatures, large and small. The study of ecology centers on patterns in distribution of plant and animal species and the reasons for these patterns. In Part 2 we...

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11. Biotic Communities of the Semiarid Foothills and Valleys

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pp. 143-158

The semiarid foothills and valleys lying between 4,500 and 9,000 feet (1,400-2,750 01) occupy the largest area of the San Juan region. We will discuss the low-lying and broadest valleys, the mesas and cuestas, and the slopes and narrow valleys of the true foothills in turn, as though there were a uniform progression from one to...

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12. Biotic Communities of the Cool Mountains

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pp. 159-174

Forest vegetation is restricted to areas of relatively high precipitation and moderate temperatures. Most of the forests in the San Juan Mountains are dominated by various species of evergreen coniferous trees. Evergreens are especially well adapted to environments with short growing seasons (because of long...

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13. Wetlands, Riparian Habitats, and Rivers

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pp. 175-189

Moisture is one of the premiere limiting factors for plants and animals' and where moisture is not limited one finds very distinctive communities of drought-intolerant species. Wetlands, defined as areas that remain moist through all or most of the growing season, include communities such as marshes and bogs. A special type...

Part III: Human History along the San Juan Skyway

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14. The Foragers of the Forest

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pp. 193-200

In this chapter I will present a description of the archaeological evidence for occupation of the San Juan Skyway area by mobile hunter- gatherers (sometimes called foragers) (Fig. 14.1). Prior to the development of agriculture, hunting and gathering was the only subsistence strategy practiced in the Four Corners region. Even...

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15. The Anasazi: Prehistoric Farmers

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pp. 201-214

Two major groups of prehistoric peoples inhabited the San Juan Skyway region, the Archaic and the Anasazi. Of the two, the Anasazi are by far the better known (see Fig. 14.1, p. 192). Visitors flock from throughout the world to see the famous cliff dwellings at Mesa Verde, the silent stone cities at Chaco Canyon, and the...

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16. The Spanish

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pp. 215-224

Long before Anglo-Americans visited the Southwest, the area was explored and settled by the Spanish. In 1540, almost seventy years before the founding of Jamestown or the landing of the pilgrim fathers at Plymouth, Francisco Vasques de Coronado led an exploring expedition into the Southwest that took his men from western...

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17. The Utes

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pp. 225-233

When the Spanish arrived in the Southwest, the people they called the Yutas, or Utes, ranged across much of present-day Colorado, northern New Mexico, and Utah. According to anthropologists, the Utes were organized into loosely defined bands, but the basic social unit was the extended family, which could most efficiently...

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18. The Miners: “They Builded Better Than They Knew,”

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pp. 234-246

They intrigued the Spanish, lured the fifty-niners, and provided a home for several generations of eager prospectors and determined hard-rock miners. To all of them they were known as the San Juan Mountains. Some of Colorado's highest and most rugged peaks insured a challenge for anyone who sought to wrestle their mineral...

Part IV: Points of Interest around the Western San Juan Mountains

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19. Points of Interest Along the San Juan Skyway

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pp. 249-347

This road guide is meant for the visitor who wishes to delve into the geology, ecology, archaeology, and history of the San Jnan Skyway region. The guide is designed to be flexible so that a traveler can enter the highway at any point and circle the loop in either direction. The points of interest are identified on topographic maps...

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20. Points of Interest Along the Durango-to-Silverton Narrow-Gauge Railroad

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pp. 348-350

The mournful whistle of the narrow-gauge train echoes between the canyon walls as much today as it did in 1882, when service began between Durango and Silverton. The train ride is only 46 miles, but it takes more than three hours to complete. From Durango to Rockwood follow the log given for the highway...

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21. Points of Interest Along the Alpine Loop

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pp. 351-363

The Alpine Loop provides easy access into the lofty San Juan Mountains and offers the inquisitive eye an "unequaled field for the observation of the processes of nature." There are no milepost signs along the Alpine Loop; therefore, points of interest are located by odometer readings beginning in Silverton. The traveler is...


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pp. 365-372


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pp. 373-376


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pp. 377-406

E-ISBN-13: 9781607321316
E-ISBN-10: 1607321319
Print-ISBN-13: 9780870813788
Print-ISBN-10: 0870813781

Page Count: 406
Illustrations: 50 b&w photos, 23 maps
Publication Year: 1996

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Subject Headings

  • Geology -- San Juan Mountains (Colo. and N.M.).
  • San Juan Mountains (Colo. and N.M.) -- History.
  • San Juan Skyway (Colo.) -- Guidebooks.
  • Ecology -- San Juan Mountains (Colo. and N.M.).
  • San Juan Mountains (Colo. and N.M.) -- Description and travel.
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