Welcome to the Virtual Field Trip: Geologic Lessons in the Northern California Foothills! This field trip takes place in the foothills east of Chico, California (about 80 miles north of Sacramento and about 150 miles north east of San Francisco).

This unusual location is an area where three distinct geologic regions come together: the southern end of the Cascade Range, the northern end of the Sierra Nevada mountains and the Sacramento Valley. What makes it interesting and unique from a geological perspective is to see the geologies of the two great west coast mountain ranges converge in a single place. Only along this narrow corridor is it possible to view both Cascade and Sierra Nevada geology simultaneously.

Geological Context

To gain a greater appreciation for the rock formations that you will see in this field trip, it will help to understand the history and nature of the three geologic regions in the area.

Cascade Range

To north and east of the field trip location, we find the southern terminus of the Cascade Range. The Cascades are a series of volcanic peaks stretching from Washington state south to Mt. Lassen. The Cascade volcanoes have formed due to the subduction and melting of the Juan de Fuca Plate. The melting of this plate has caused hot magma to well up and erupt, forming a series of volcanos. Mt. Lassen, just to the north of the location of this field trip, is the southernmost volcano in the Cascade Range. We see some of the volcanic rocks typical of the Cascades in the area of the field trip in the volcanic mudflows of the Tuscan Formation. Another older volcanic event in the field trip area isd represented by the basalts of the Lovejoy formation.

Sierra Nevada Mountains

The Sierra Nevada are known for such outstanding features as Yosemite Valley, Lake Tahoe, the General Sherman Tree and Mt. Whitney (the highest point in the US outside of Alaska). This trip, located at the relatively gentle northern end of the range, lacks high peaks and dramatic granitic outcrops.

The Sierra Nevada batholiths are large intrusions of magma that cooled within the earth 80 to 200 million years ago...

Though most of the high Sierra Nevada is made up of granitic rocks, the western foothills of the range are often made up of paleozoic rock that were metamorphosed by the heat and pressure generate by the intrusion of the Sierra Nevada batholiths (we will see some of these rocks in this field trip in the Basement formation) or sedimentary rocks deposited on the metamorphic rocks by an ancient shallow sea (we will also see some of these rocks in the Chico formation).

Sacramento Valley

To the west of the field trip area, are the sediments of the Sacramento Valley. The Sacramento Valley forms the northen half of the Great Central Valley of California. This area has been a site of intermittent deposition for the past 100 million years. Both marine and non-marine conditions have existed in the valley. Some of the accumulated sediments that have occurred over the past 13 million years are directly related to the uplifting erosion the Sierra Nevada.

Learning Objectives

The primary objective of this field trip is for you to gain a better understanding of and appreciation for the geology of the northern California foothills.

More specifically, once you have completed this field trip you should:

1. Understand and recognize the types of rock formations (and their component rock types) found at each location
2. Understand the geologic forces that created the rock formations found in each location
3. Understand the spatial and temporal relationships between the different geologic formations found in each location
4. Be able to assemble a complete geologic timeline for the area based on the partial timelines found at each location

Tracker

Keeping Track of Your Progress

For the most part, this site functions like any other web site. You are free to explore each of the three field trip locations in any order that you wish. In order to help you keep track of what you've learned, a special tool has been added to the site that allows you to place geologic formations in their proper place in the timeline. Since no single location contains a complete geologic timeline, the Tracker (right) allows you to place each rock formation at its proper place in time. As long as you don't close the Tracker window, it will keep track of each formation. When you believe that you have all the formations in their correct locations in time, you can click on "Check my work!" to see whether you got each formation correct.

To access the "Tracker", click on the "Whatever" button at the top of any page. To get help on using the Tracker, click on the "Help" button in the upper right-hand corner of the Tracker window.