Tuesday, August 07, 2007

Visiting the Wenas mammoth

Last summer when I read a large Associated Press story about the excavation of a mammoth on Wenas Creek, I was very excited. Wenas Creek is on the way to Mom's house; I drive by the mouth of the creek at least once a month. Maybe, I thought, I can visit, or volunteer, or hang out and become their new best friend.

But then my excitement turned to disappointment. The big article that the local paper ran on it was published the week after the dig closed for the season. I've waited most of the year for the dig to reopen and a few weeks ago it did. I finally visited the site three weeks ago and here is my report.

Wenas Creek flows into the Yakima River from a point in the Cascade Mountains about thirty miles due northwest of the small town of Selah. For most of its length the creek has a wide bottom that is the home to dozens of neat and orderly horse ranches. The ridges on either side of the valley are dusty and covered with sage and dry grasses.

Approaching the dig with Wenas Creek Valley in the background.

In the Spring of 2005, Mayo Ranches hired the Gary Fife Inc., a local construction firm, to build a new road up a hill on their property. Near the end of the project, the Fife workers decided to scrape some earth from the uphill-side of the road to level a dip in the road. A few feet below the surface the backhoe operator uncovered something that looked out of place. Most of the soil on the hill was dry and light colored with a layer of water rounded rocks beneath. What he found was a large irregular and yellowish object just above the rock layer. Fortunately for us, it was lunch time so the construction crew stopped to look at the odd object. Even though the backhoe had damaged the object, it was clear that they were looking at the end of an enormous leg bone.

They told the owners that they had found a dinosaur and the owners called Central Washington University in nearby Ellensburg and eventually contacted Morris Uebelacker of the Department of Geography. Uebelacker showed the bone fragments to Patrick Lubinski of the Department of Anthropology, who recognized it as a mammoth humerus.

At this point let me digress to mention the Lake Missoula floods. I've written about these before. From about 16,000 years ago till about 12,000 years ago Eastern Washington was regularly scoured by some of the largest floods to happen on this planet in the last few million years. These pose a special challenge for paleontologists. This means that most of the Pleistocene bones in the region have been scattered by flowing water. That doesn't mean that there is no information to be gained from these bones. George Last of the Pacific Northwest National Laboratory at Hanford is building a database of the spread of bones in order to map some of the activities of the flood itself. But that's not what interested the CWU professors about the Wenas mammoth.

The Wenas mammoth is about one hundred feet above the highest of the Missoula floods. The floods probably reached the mouth of Wenas Creek. The mammoth on the Mayo ranch is about fifty feet above the valley bottom and about three miles from the confluence of Wenas Creek and the Yakima River. This means the Wenas mammoth bones were not affected by the floods. No mammoth in Eastern Washington has been excavated where it died. The Wenas mammoth is a first for the region.

Drs. Uebelacker and Lubinski were able to form a team and start excavations that same year. This year is their third season. The excavation has been able to precede slowly because it is not threatened by development. Far too much archaeology and paleontology is conducted as an emergency evacuation ahead of bulldozers. The Mayo family have no plans for the hillside where the mammoth was found and support the University's scientific mission. Mrs. Mayo created the mammoth illustration that has become the logo for the dig. This is excellent community outreach on the part of the University.

Mrs. Mayo's logo.

So what did I see when I drove up the dusty side road to the mammoth dig?

Of course I got lost on the way. I headed up the wrong valley, then turned back and found my way into Wenas Creek. I slowed down to read signs and almost immediately found Mrs. Mayo's sign. A few hundred yards up the dusty side road and up the hill, the road leveled out to reveal a group of tents. I almost fell off the road in my excitement. I parked and ran back to take pictures of the signs on the road.

A guide tracked me down as ran around like a sugared up eight year old and pointed me to the guest tent. She told me that the next tour would begin in about fifteen minutes, that I could sign the guest book, and look at their informational display while staying out of the sun. Hot weather and I are not friends. I already came prepared with a hat, dark glasses, a light shirt, and a half-gallon of ice tea. I took a few more pictures and checked out the tent. The guest book revealed that the site was getting seven or eight visitors per day. The informational display was professionally done, but the tri-fold signs reminded me of a grade school science fair or a small town museum. I have never been to scientific conference, so I have never seen the posters that minor contributors put up. I wondered if this is what they are like, or if they are more like a term paper glued to the wall. In any case, the tent display answered some of my basic questions while provoking new ones.

The work tents.

A couple, a few years older than me, arrived just before the tour should have begun. They were local ranchers who wanted to see the site, more out of civic pride than anything else. I waited while they checked out the information tent, then our guide arrived and we crossed the road to the main excavation. She told us about the background to the dig, which I have retold above, then she took us to the active pits.

A couple of students were working in one of the pits under the direction of Bax Barton, the team paleoecologist, while Dr. Lubinski and another student walked around planning the next stage of work. Barton joined us to answer questions.

Paleontological and archaeological digs all pretty much look the same: a series of precise 2 x 2 meter square holes in the ground with people intensely scraping thin layers of soil away. The workers carefully study the ground that they are removing and then send their soil to another worker who shakes it through a wire screen. Everything they find is carefully documented. The pits are surrounded by various measuring sticks (and now GPS units), paint brushes, and note taking tools, which these days include laptops, digital cameras, along with the traditional notebooks and stubby pencils. At Wenas, the soil is very dry and crumbly, so it's fairly easy to remove, but it is also very dusty to handle. I was still sucking grit off of my teeth an hour after I left and long after I finished my iced tea.

Looking into the pits, we could see three clear layers of soil. The topmost layer is light colored and finely grained. This is mostly wind deposited. In some places a white streak was visible just below the surface. This was ash from the 1980 eruption of Mt. St. Helens. Ashfalls like this are quite valuable because the isotopes can be used for radiometric dating. The next layer down was darker and a bit coarser grained. This, our guide told us, was gravity deposited, by which I assumed she meant mud from further up the hill. The lowest level that they were working was made up of round rocks, the sort that you find in river and creek bottoms. That's exactly what they were. Barton used a folding measuring stick to point out the layers for us and to indicate out a few bone fragments that hadn't been removed yet. As I mentioned above, the mammoth bones were found on top of the rock layer.

Bax Barton does his best Vanna White imitation while pointing out the main strata. The flags mark finer delineations among the three strata that I mention. The rough areas near the bottom are shelves containing bones that they have not yet removed.

In the past two years they have found the front limbs of the mammoth, some neck vertebrae, ribs, and both shoulder blades. They have not found the rear half, the skull, or the tusks. The latter led to a bit of a running gag. Early on I asked how old the mammoth was when it died. Our guide said that it was an adult, but that they couldn't give a more precise estimate of its age without the teeth or tusks. Did they know whether it was a male or female, I asked. Not without the tusks. When she explained the differences between the Columbian and woolly mammoths, my companions asked which one this was. She paused and they jumped in, oh, you need the tusks.

So far, they only have this middle portion of the mammoth. They still haven't discerned a pattern in the spread of the bones. If a mammoth died of natural causes or was killed by predators, the bones might be scattered over a fairly large area by scavengers. If it was killed by humans and butchered, we might find the top side missing and the bottom side still in place or scattered by scavengers. If the mammoth drowned, was buried by a mudslide, or otherwise died in a place inaccessible to scavengers, we might find the entire skeleton close together and even fully assembled. While I was there, they were starting a pit on the downhill side of the road to see if any bones have spread that far. The worse case scenario, which no one was mentioning, is that the skull and tusks are right under the road.

One tantalizing clue about the site is a rock chip that they found last year. This is a flake of chert, almost certainly produced by human tool making. It was found an inch or so above one of the forelimbs. That inch might mean a couple thousand years or the same day. They don't have enough data yet to make a date determination on the chip. The bones themselves have been dated by multiple carbon -14 tests to 16,000 years ago (which is about when the first Missoula flood happened).

The ribs of a bovid animal, probably a buffalo of some sort, have been found with the mammoth's. This is another clue about the origin of the bones. If the human link is confirmed, it will probably mean that this was some kind of kill site, like a water hole or mud wallow. It could also be evidence that the animals died elsewhere and had their bones moved here by flowing water or mud. They might be mixed together for no other reason than that this was once a bend in the creek.

After showing us a few other operations, we dropped by the pit that was the star attraction that day. On an unexcavated shelf near the bottom of the pit was exposed a split scapula, a shoulder blade, of the mammoth. The blade was about the size of a serving platter. One end of it extended into the pit wall. While the bits of ribs that we had seen in the previous pits didn't look that different from a splintered stick, this was clearly a bone--a big bone.

The scapula. A cow's scapula is on the right side of the pit for size comparison. The student in the center is beginning to move the wall between this pit and the next so they can remove the scapula. In the foreground you can see the string markers for the next pit, which they might have been able to start if I wasn't standing in the middle of it taking pictures.

While we admired the scapula, Barton mentioned that they had just shipped off their grant applications for next year's work. The Mayo's are happy to let the University excavate for years to come, but the University has to beg from season to season to keep the work going. Many of the tools and other supplies, such as the paintbrushes, have been donated by science-minded local businesses.

There are a number of good reasons why this did should be funded. As I mentioned above, this is the first mammoth in the region to be excavated that was not scattered by the Lake Missoula floods. As such it is the best possible teaching dig for the students of CWU. Mammoths are common enough that a bone by itself isn't that interesting. We already understand mammoth anatomy. The most interesting information we can gain from most mammoth discoveries is that which can be gleaned from their context.

The best example of context is the rock chip. If that chip can be associated with the mammoth it will mean that people were in the Northwest thousands of years earlier than was previously thought. The leading theory of the peopling of the Americas was that Siberians entered North America through Alaska and walked into the center of the continent as the glaciers pulled back. In recent years some evidence has appearaed that put humans here too early to have come that way. The best alternative is that they still came from Asia and touched on Alaska, but came down the west coast in boats. A confirmed 16,000 years old tool in Washington would add huge support to the coastal migration theory. It would also mean that there were human witnesses to the Missoula floods, which is just mind boggling to imagine.

Even if the tool doesn't pan out, there is a lot to be learned from a mammoth in that year. Sixteen thousand years ago was right about when the climate was rapidly turning warmer. The mammoth skeleton can tell us many things about the kind of environmental stresses that climate change produced (unfortunately, tusks are one of the best bones for this). The soil that buried the mammoth will contain valuable clues to the climate in the form of pollen and other botanical remains.

The dig now has a web cam which will be broadcasting for the week or so left in the season. After that, they will cover the dig, unplug the camera, and remove the signs so the Mayos can have some privacy for the rest of the year. Then the team will return to Ellensburg to prepare for the fall semester. But that's not the end of the story. digging up the bones is just the start of their work. During the winter they will be going over soil samples with microscopes and performing as many test as they can imagine. And I'll keep watching for news out of Ellensburg.

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