River Watcher: The Clay Connection

Near the Diversion Dam at Oroville after a spring rain, I discovered a puddle rimmed with a photogenic film of yellow pine pollen. In the process of getting close, I stepped into gummy clay mud, and the Nike rippled soles were plastered as I skidded my way to solid ground.

Clay! That type of soil is like a mixture of glue-stirred, pliable slick manure, as a ceramist well knows, but fortunately, water, nature's greatest solvent, comes to the rescue. Let clay dry, though, and you have a brick or yellow caked shoes, or it can be permanently hardened by firing in a kiln to make pottery.

According to geological summaries, the Earth was a mass of melted magma for the first two billion or so years after its creation until it finally cooled down into solid rock. At least on the surface. The hot liquid magma lurks beneath the crust at our feet!

Until living creatures got into the act with organic matter, rock ruled, and erosion contributed pulverized pieces to the formation of future soils. Clay is essentially fine-ground rock-minerals containing trapped water molecules, which may be mixed with sand, loam, and loess to form various degrees of soil — the foundation of life.

I think of clay bluffs in my homeland of Northern Missouri. Bunker Hill and Foxden Bluff were mounded hills of secondary clay; composed of smashed glacial gravel drift called glacial till, but I loved to explore those eroded "mountains" and find transported Lake Superior agates, spruce fossil wood, and rocky oddities from far away places.

The creamy colored brick stamped "Mo-Rex" that I have, is fire-brick from Mexico, MO.

Great granite erratic boulders had been shoved far from their origins, and the glacier weight pulverized rock to glacial flour, hence clay. Some of that ice mass was 13,000 feet thick and was like a giant bulldozer. The last Ice Age was about 10,000 years ago, and in three million years there were 30 ice sheet ages fingering across the Midwest to as far south as the Missouri River, and down the spine of the Sierra Range into Yosemite.

Clay that remains in place is called primary clay, and is not infiltrated with till impurities, making it highly desirable for potters to work the fine textured clay. The purest form is called kaolin, used in delicate porcelain. The word Kaolin comes from Kao-ling, China, famous for Chinaware made from the kaolinite aluminum silicate mineral clay combination found there.

In the silica sand removal in Table Mountain's Morris Ravine, pockets of primary clay were found in the sand, and it was pumped into a retaining pit. Ceramist Richard Harvey gained permission to take some of the Artists of River Town there to obtain a few buckets of the grayish clay. You don't want to get stuck in that sticky stuff or you'll sink and be stranded!

Some clay trivia: Clay has been used in construction as bricks and pottery since 6000 B.C. Clay mixed with straw and sun-dried forms adobe bricks. The tile roof on the Feather River Nature Center is fired clay, as it was in the original 1935 building. The core of Oroville Dam is clay transported from the "Clay Pit" southwest of Oroville.

On my desk I have a block of catlinite, or Indian pipestone, bought at Pipestone National Monument in Minnesota by my cousin Al Tolle. Several tribes quarried the very fine soft clay that is wedged between layers of very hard Sioux Quartzite. The argillite metamorphosed mudstone contains kaolinite, making it suitable for pipe-making, as in Native American 'peace pipes'.