Sunday, May 15, 2016


Are you lucky enough to live near a river? For much of my life I didn't have that privilege. Southern California has creeks at best, except when they were flooding and otherwise causing havoc. The creeks often flowed through incredibly beautiful mountains and valleys, but they can't be a source of life for human civilization. We're too busy using what little water there is that there is barely enough to maintain a healthy ecosystem. Southern California has to import around 85% of the water that it uses.
People who live in Northern California or the Pacific Northwest might smile when I describe my Tuolumne as a river. Compared to the mighty rivers like the Columbia it is a middling stream. The thing is, it lies about that point in the northward journey in California where the rivers provide sufficient water for local use that it doesn't have to be imported from elsewhere (indeed, much of the water from the Tuolumne is exported to the Bay Area). We depend mostly on groundwater for domestic use, and the groundwater is replenished in part by the river. Most of the river goes to irrigation, but some is allowed to flow into the San Joaquin River and on to the ocean (not willingly, it should be noted; there are some who would just as soon use all of it).
The Tuolumne River begins high in the Sierra Nevada, flowing through Tuolumne Meadows in Yosemite National Park. It plunges into the Grand Canyon of the Tuolumne, a spectacular gorge that is as deep as that other canyon in Arizona. It is briefly stopped and diverted at Hetch Hetchy Reservoir, and then flows through a lesser-known gorge (unless you are a rafting enthusiast) to Don Pedro Reservoir. More water is siphoned off, but part of the river continues through the Sierra Nevada foothills and Mother Lode, and finally flows into the Great Valley, where it joins with the San Joaquin.
A swallow swings low over the river.
That's where I found myself today, rafting a section of the Tuolumne where it flows through the foothills between La Grange and Turlock Lake State Recreational Area. I had joined the Tuolumne River Trust on their By Land and By Water Canoeing trip, where I was serving as the resident geologist (literally 'resident', as I live just ten miles downstream). It was a fine adventure for the twenty or so participants, who were helping raise funds for the Trust.

What do they do? The Trust organizes river clean-ups, restoration of regions burned by the Rim Fire, and educational opportunities for children and adults. They also do political advocacy, as a voice for the river itself in the cacophony of agricultural and urban water interests. It's a great organization that deserves your support!
The river was alive with birds, bugs and amphibians. I glanced at a bug hovering a foot or so over the river, and it suddenly disappeared in the mouth of a swallow. The swallows accompanied us along the entire length of our journey. Maybe all the oars hitting the water was stirring up the bugs! I saw an old telephone pole in the distance, and immediately recognized the huge pile of sticks and random debris as an Osprey nest. Both parents were there, along with at least one chick (barely visible to the right of the birds in the picture above).
The Ospreys were not happy with the rafters and canoers below, and let them know in no uncertain terms. They relaxed when we floated by and headed downstream.The river is a perfect habitat for these grand birds. 90% or more of their diet is fish, and they are experts at landing feet-first in river to grab unwary ones floating near the surface.
Exposure of Valley Springs Formation along the Tuolumne River
There is some interesting geology on the lower river. The cliffs we passed had outcrops of white or tan-colored volcanic ash called the Valley Springs Formation. The ash was the result of gigantic eruptions of rhyolitic magma at calderas located in central Nevada! Given the media fascination with Yellowstone "super-volcanoes", people might be surprised to find that similar calderas erupted all across the American West between 20 and 30 million years ago.

A bit further downstream there are exposures of the Mehrten Formation. It originated from volcanic mudflows related to the Cascades-style stratovolcanoes that once existed near the present day summit of the Sierra Nevada around 10 million years ago. Sediments within the unit have yielded an array of fossils including ancient camels and horses, giant tortoises, and strange 8 foot long saber-toothed salmon! Younger rocks above the Mehrten have given up Mammoths, Mastodons, Saber-tooth Cats, American Lions, Short-faced Bears, and Giant Ground Sloths, along with many other ice age species.
The lower reaches of the Tuolumne River cannot be mistaken for a world class whitewater rafting locale (you have to go upstream for that), but it can present unique challenges to amateur canoeists like myself. There are thickets of willow and cottonwood trees along the banks, and sudden turns in the river course can drive boats into a maze of branches. We had half a dozen swampings that usually happened when both canoeists ducked in the same direction as they went into the thickets. No one was hurt, but it can be momentarily terrifying.
In some places the river was constricted to where it was only a few feet wide, and the water flowed very fast. If you look at the canoe above, you can see how fast it's plowing through the water as the people oared furiously to avoid the thicket just below. The water whipped them in a circle into a back eddy.
There were also hazards caused by fallen trees. Some of them reached almost across the river, and the one above occurred just after a fast-moving chute. Being short (which I'm not!) has advantages in such situations. The Trust folks put a premium on safety. You can see that everyone had a personal flotation device, and leaders were stationed at critical points in the difficult passages to help guide boats through.

We've abused our rivers. Gold dredges did incalculable damage to this stretch of the river by ripping out the riparian vegetation and destroying the soils along the river floodplain. Miles of river habitat were destroyed by the search for a few suitcases of gold, but money seems to trump all. Over the decades the river has started to recover, but it will be many more years before the river can be truly healthy for salmon and all the other life forms that historically lived along the river (I looked for River Otters today, but unfortunately didn't see any). There are many other challenges, like the invasive hyacinth, a water plant that clogs river channels, pollution (why do we use rivers as a dumping ground?), and low flows related to the continuing drought in California (the water is warmer than it should be).
It was a marvelous day spent with people who are working hard to protect and rehabilitate this precious resource. Rivers are truly a gift, and they need to be cherished and protected. What rivers are near you, and what can you do to help?


The Field of Gold said...

At my back gate is the Kawarau River. It's a major although I am not sure of the Cumecs. Possibly the size of the Colorado, and when it joins the Clutha just 5-6 Kms downstream it doubles at least.
The stretch of river here of about 3-4 kms was the home of the gold dredge "Lady Ranfurly" 1902 to 1918. Said to be the worlds most successful ever

Anonymous said...

I've mentioned I spent my youth riding along the Santa Ana and San Gabriel "rivers". These pictures are beautiful Garry. You've almost convinced me to relocate to Modesto :)

Jane Foster said...

I live nearby Colorado river so I organize the whitewater rafting trips with my friends who visit every once in a month. It's awesome fun and everyone must experience it once.