Bidwell Park

Introduction

Bidwell Park, located east of the city of Chico (map), is one of the largest municipal parks in the United States. Chico Creek flows through the park and has carved a deep canyon in its headwaters. The canyon has exposed rock formations dating as far back as 90 million years for our examination, including rock formations not found elsewhere in this virtual field trip. These formations provide indispensable clues toward gaining a complete understanding of the geologic record of this area of northern California. Even with these clues, however, there are several large gaps in the Bidwell Park sequence that can only be filled by visiting other locations in this tour.

• Geology
• Photographs
• Related Links

Geology

The sequence of rock formations in the Bidwell Park area are:

Chico Formation: The oldest rocks in the park are those of the Chico formation which can be seen at the east end of the park. The Chico formation consists of sandstone, siltstone, thin layers of limestone, and conglomerate, all of which accumulated along the shore of the ocean during the Cretaceous period of the Mesozoic Era. Evidence that the sands of the Chico Formation were deposited in the ocean is provided by fossils of clams, snails and other marine organisms that have been collected from the sandstone layers. (Learn more...)

Rock outcrops of Tuscan formation breccias.

Lovejoy Formation: A thick, black lava-flow is well exposed throughout eastern Bidwell Park, which is named Lovejoy Basalt. Basalt is a hard, black, smooth rock and is one of the most common types of lava erupted by volcanoes. Lovejoy Basalt rests unconformably on the Chico Formation. "Unconformably" means that there was a large interval of time between deposition of the Chico and the eruption of the Lovejoy. (Learn more...)

Tuscan Formation: The material that forms the Tuscan Formation consists of a number of layers of breccia and conglomerate. Some of these layers were deposited by streams but the majority of the deposits are from volcanic mudflows. The particles embedded in the breccia and conglomerate are volcanic in nature. The mudflows spread out over the area burying older rock, filling low areas and gradually building a flat subdued landscape. The latest uprising of the Sierras titled the rock layers westward creating the geologic conditions that provide the water supply for Chico. (Learn more...)