Bear Granite - UCSD EarthCache

Welcome to UC San Diego

The UC San Diego campus is home to many unique public art installations, including Bear by Tim Hawkinson. At first glance, this massive stone sculpture may seem like a playful figure assembled from boulders. However, it is a carefully engineered artwork that balances whimsy with geology, inviting viewers to reflect on the intersection of nature and human creativity. This EarthCache invites you to investigate the granite’s origins and how erosion shaped its surface

Formation of Granite

Granite forms deep within the Earth’s crust through the slow cooling of magma, a molten rock rich in silica, aluminum, and other elements. This process occurs in large underground chambers called plutons, where heat and pressure remain high enough to allow minerals to crystallize over millions of years. The cooling happens gradually, which lets crystals grow large enough to be seen with the naked eye, giving granite its coarse-grained texture. Different minerals crystallize at different rates depending on their melting points and chemical makeup. Quartz, feldspar, and mica are the most common minerals, with quartz forming glassy, light-colored grains, feldspar producing blocky crystals that can vary in color from pink to white, and mica appearing as dark, shiny flakes. Sometimes granite also contains small amounts of hornblende or other accessory minerals, which reflect subtle differences in the chemical composition of the original magma. These variations in mineral content not only influence the color and hardness of the granite but also provide clues about the temperature, pressure, and chemical environment deep in the Earth when the rock formed.

Over millions of years, tectonic forces and erosion expose granite that was once buried far below the surface. Uplift from mountain-building processes can push granite plutons upward, while erosion from rivers, glaciers, and wind gradually removes the overlying rocks. As the pressure on the granite decreases during exposure, the rock can expand and fracture, forming characteristic sheet-like layers or rounded domes through a process called exfoliation. The specific appearance of these features often depends on the mineral composition and crystal size of the granite. For example, granites rich in quartz are more resistant to weathering, so they tend to form prominent cliffs or boulders, while granites with higher mica or feldspar content can weather into finer soils more easily. These differences in durability and erosion patterns mean that the way granite appears at the surface reflects both its original formation deep underground and the environmental conditions it has experienced since exposure.

Granite is also an important record of the Earth’s geological history because its mineral composition and texture reveal conditions in the crust at the time of formation. Variations in mineral proportions indicate differences in magma chemistry; a granite with abundant quartz and feldspar suggests a high-silica, low-iron magma, while one with more dark mica or hornblende reflects slightly more iron and magnesium in the magma. Crystal size and arrangement reveal cooling rates, with large, well-formed crystals indicating very slow cooling over millions of years, and smaller, less distinct crystals pointing to faster cooling or more complex crystallization histories. Studying these features helps geologists understand not only how granite formed but also the broader tectonic processes shaping continental crust, such as magma intrusion, mountain building, and crustal recycling. Granite’s durability, distinct textures, and chemical diversity make it both a prominent feature of landscapes and a detailed record of Earth’s deep, dynamic interior over billions of years.

Spheroidal Weathering in Granite

Granite is susceptible to a specific form of chemical and physical weathering known as spheroidal weathering. This process gradually rounds the edges and corners of angular rock blocks, producing a smooth, curved surface over time. It occurs when water infiltrates natural fractures or joints in the granite and initiates chemical reactions such as hydrolysis and oxidation, particularly affecting minerals like feldspar. Because the outer layers are exposed to weathering on multiple sides, they deteriorate more rapidly than the interior, resulting in a characteristic concentric or “onion-skin” pattern. Spheroidal weathering is especially common in granitic landscapes and contributes to the development of rounded boulders and dome-shaped outcrops.

Tasks for This EarthCache

To log this EarthCache, visit the site and complete the following tasks. Send me your answers via Geocaching or email.

1. Include "Bear Granite - UCSD - GCB8ZNZ" on the first line of your message.

2. Observe the color and texture of the granite used in the sculpture. Which minerals can you identify, such as quartz, feldspar, or mica? Estimate the relative amounts of light-colored versus dark-colored minerals

3. Look closely at the size of the mineral crystals in the granite. Are they large and easily visible, or small and harder to distinguish? What does the crystal size tell you about how quickly the granite cooled when it originally formed underground?

4. What signs of spheroidal weathering can you observe on the granite surface today? Explain what this suggests about how the rock weathered over time.

5. In your log, attach a photo of yourself or a personal item with the Bear sculpture in the background. (Note: photos predating the publication of this EarthCache are not accepted.)