Columns of the Giants EarthCache

Welcome to Columns of the Giants!

Experience unique geology on this easy half-mile walk. This self-guided trail reveals a brief chapter in the dynamic history of the Sierra Nevada. Discover how forces of nature created and sculpted these columns of stone.

Shaped by Fire and Ice

About 150,000 years ago, lava from deep within the Earth, erupted from a nearby crack.  The lava flowed into the Stanislaus riverbed and pooled behind a natural dam.  As this deep pool of lava slowly cooled, the molten rock hardened and shrank – splitting into multi-sided vertical columns.

Later, a glacier flowed down this valley.  Gravel in the ice acted like sandpaper, scratching the top while plucking and ripping rocks from the bank, exposing the columns.

But, wait. Let’s back up a bit. How exactly do these columns form?

Columns of Basalt

Basalt is an igneous, volcanic rock. For those of you who need a little Geology 101 refresher, “igneous” means that the rock formed from a melt and “volcanic” means that the melt erupted at the Earth’s surface as lava before it cooled to form the rock. After lava is erupted onto Earth’s surface, it cools. However, lava may take awhile to cool, and as it cools there may be a temperature gradient. Most commonly, the top of the lava flow will be cooler than the bottom of the lava flow.

Columnar Jointing

Columnar jointing is a geological structure where sets of intersecting closely spaced fractures, referred to as joints, result in the formation of a regular array of polygonal prisms, or columns. Columnar jointing occurs in many types of volcanic rocks and forms as the rock cools and contracts. When objects contract, they often crack or fracture. When contraction occurs at centers which are equally spaced (see the above diagram), then a hexagonal fracture pattern will develop. This relatively equal spacing in the fractures of the lava flow is most likely to occur in lava flows of uniform thickness and composition. If the contraction is not evenly spaced, then other geometries of fractures, such as 5-sided or 7-sided fractures, may occur. Contraction may not be equally spaced if, for example, the thickness or composition of the lava flow varies widely. The fracture pattern that forms at the cooling surface will tend to be propagated down the lava as it cools, perpendicular to the top of the lava flow, forming long, geometric columns. These columns form in a variety of sizes– some are fairly small, and some are wider and much taller than people! The columns can vary from 10 feet to a few inches in diameter, and can be nearly 100 feet tall!

Other Famous Examples of Spectacular Columnar Basalt

Giant's Causeway, County Antrim, Northern Ireland
Fingals Cave, Staffa Island, Scotland
Columbia River flood basalts of Oregon, Washington, and Idaho, USA
Devils Postpile, California, USA
Devils Tower, Wyoming, USA

Basaltic columns are typically parallel and straight, but can also be curved and vary in diameter. Whereas an array of regular and straight columns is called a colonnade, an irregular array is termed an entablature. Entablature jointing is usually observed in more viscous (thicker) flows that cooled under less uniform conditions. The entablature portion displays a pattern of numerous, irregularly jointed, small columns to randomly oriented cooling joints that abruptly overlie a thinner colonnade flow displaying well-developed columnar jointing. The transition zone between the entablature and the basal colonnade may be very narrow, generally less than 0.5 ft in width. Typically, the entablature is thicker than the basal colonnade, often comprising at least two-thirds of the total flow thickness.

Getting to and successfully logging this earthcache will take you on a pleasant half-mile round trip stroll, crossing the Middle Fork of the Stanislaus River, along a paved, wheelchair friendly path. Your walk will take you to five informational signs where you must gather information to log this cache. Three of the signs you will walk by on your way out to the earthcache location. The final two signs are at the earthcache location. Take note of what you have learned on this walk, along with the things you have learned reading this earthcache description in order to answer all of the required questions.

Columns of the Giants is accessible by car in the spring, summer and fall months. State Route 108, the highway taking you to this earthcache, is typically closed during the winter to vehicle traffic just past the communities of Pinecrest, Dodge Ridge and Strawberry driving eastbound from Sonora, and just past the Marine Corps Mountain Warfare Training Center driving westbound from U.S. Route 395. You can check for road conditions and road closures here: Current State Route 108 Conditions.

Logging Requirements:

In order to log this earthcache as found, send an e-mail through our geocaching profile with the first line containing " GC5CGW9 Columns of the Giants" and then on the subsequent lines, the answers to the following questions based on your observations and information obtained during your visit to this incredibly scenic spot.

1. Place the text "GC5CGW9 Columns of the Giants" on the first line of your email.
2. Tell us the number of people in your group.
3. Evidence can be seen here of how many separate lava flows?
4. Do you see any flow structures that would be considered colonnade? Explain why or why not.
5. Do you see any flow structures that would be considered enatblature? Explain why or why not.
6. Under optimal conditions, the cooling and shrinking of the basalt results in cracks speading out at angles of how many degrees?
7. At the earthcache location (Ground Zero) you will see talus (a collection of broken rock fragments) comprised and composed of broken basalt columns. Looking at some of the fragments near the edge of the path, what would you guess is the typical diameter of the basalt columns here?
8. Optional: Post a picture with you and your GPS at the location, making sure not to give away any answers in your photo!

Do not include any answers to the above questions in your log, even if encrypted, or we will have to delete your entry. If you do not e-mail us the answers to the above questions within a reasonable amount of time your log will be deleted.