Lesson 7: Basin and Range and Mojave Deserts

Titus Canyon Anticline, photo by Marli Miller.In this week's lesson, as in last week's, we'll be studying the processes that have shaped the deserts of eastern California. Although this week's lesson emphasizes rocks that were formed long ago (like the strata exposed in the Titus Canyon Anticline, right), crustal extension and the Cenozoic sedimentation and volcanism associated with it continue to be important processes across the Basin and Range and Mojave provinces. This week we'll also begin working on the first of our four writing assignments. During the coming weeks these assignments will give you a chance to read two scientific papers that present recent ideas about California geology that are not in our text, and learn how geologists organize and interpret their observations to come up with new models for how the Earth works.

In chapter 7 Harden describes the bedrock geology of the Basin and Range and Mojave deserts. She begins by describing how young extensional faults have broken the landscapes of these provinces into parallel basins and ranges during the past 20 million years and, in so doing, produced local sedimentary basins and young volcanoes. Next, she takes us back in time to learn how rocks exposed across this region were deposited on a continental shelf formed by the break-up of an ancient supercontinent several hundred million years ago. Finally, she describes how the beginning of subduction along the western margin of North America about 225 m.y. ago crumpled the ancient sediments into folds and produced granitic magmas that were emplaced into the crust during Mesozoic time.

As you read about the complex geologic history of California's deserts it will be useful to take detailed notes. The region described in this chapter has experienced several major events—Proterozoic rifting; Paleozoic passive margin sedimentation; Mesozoic folding, faulting and intrusion due to subduction; and Cenozoic extension and volcanism—and writing out key facts in your own words or making neatly labeled drawings will help you better understand the significance of what you've read and keep everything straight. Having good notes will also make it easier for you to review for this week's quiz and and access what you've learned when you want to refer back to it for future assignments. Be sure that you are prepared to meet the learning objectives outlined below before you move on to the quiz at the bottom of the page.

Weekly Learning Objectives

Upon successful completion of this week's lesson, a student is expected to be able to:

Reading and Browsing Assignment

Exercise 7: Outline of First Article (Due by 9:00 AM on 28-Feb-2011)

This week's exercise is to complete the first of our four writing assignments. To learn about the assignment read through the pointers below and then click on the "Resources" link on the left side of this page, scroll down, and click on "Outline 1" under "Writing Assignment" near the bottom of the page. This week we'll be completing steps one and two and you'll be turning in the outline of the article you choose from the first set.

Quiz 7: Basin and Range and Mojave Deserts (Due by 9:00 AM on 28-Feb-2011.)

After you feel you have met the learning outcomes outlined above, please complete Quiz 7 in the Etudes "Assignments, Tests, and Surveys" tool. There are ten questions about California's deserts and each is worth one point. If you can answer all of them correctly it means that you know your way around ancient landscape of California's Basin and Range and Mojave deserts pretty well and are ready to start learning about one of California's most iconic regions—the Sierra Nevada—next week. Like all of our weekly quizzes, this one is timed (you'll have 30 minutes) and must be completed in one "sitting". (That is, you will only be granted access once.) So, be sure you're ready to complete your quiz when you start it—and be sure you're using Firefox. Good luck.