Natural Trap Cave: First instalment of year 1 of the field project.

by Alan Cooper

Having rigged the cave on the first day, I guess it was appropriate that I was the one to take the first descent into the chasm below. It’s caving lore something along the lines of the Captain going down with his ship – if you rigged it, you should be first to ‘test’ it out! Backing over the ledge and unlocking my brakebar, I descended about 3 m against a series of ledges – before dropping into open space. Looking around I could see several enormous nests, around a metre wide and made of big branches – eagles had obviously lived under the overhang of the cave entrance for many years, presumably until the grid was placed over the entrance. I’ve not seen eagle nests up close before and it was impressed how large they were. Pack rats were also nesting around these ledges – 100ft over space, and we saw several snake skeletons down in the cave attesting to the effective security systems surrounding their home!

Letting the rope run around my backside and through my brakebar, I slowly dropped into the middle of a huge chamber – several hundred ft in diameter, lit up by a narrow beam of sunlight streaming through the entrance above onto a patch of floor. I could see we weren’t going to need our caving lights for much of the day, as much of the giant chamber was quite bright due to the reflected sunlight. The temperature didn’t feel like the 5’C we’d been warned about (although this did in fact turn out to be the ground temperature) and the chamber itself was quite impressive. Huge blocks had dropped off the roof on one side, I was dropping into a deep pit in the middle of the cave floor, which turned out to be the collapsed remains of the original excavations from 1975-1984. My comment on the walkie-talkie to the surface team was ‘It looks like a f***ing WWI re-enactment…’ – as the walls of the original excavations had collapsed due to erosion from water and snow coming in the entrance, forming the large pit. It is standard practice to backfill any archaeological excavations, to minimise disruption to the surrounding sediments and for safety, but back in 1984 this was not yet established.

After landing, and marvelling at the detritus and old trench faces, one of the highlights was the top two runs of an aluminium ladder sticking straight out of the ground – indicating that the original 1984 trench was down at the bottom of the ladder, but 30 years of sediment had completely filled it in! That would be a huge volume to re-excavate! I figured I should return to the surface to report – and also to check out what the ascent was going to be like for the novices. The new ropes were annoying as they tended to spin around when weight was applied to them – coiling the safety and main lines. In the end I had to leave one hand above my top jumar just to push the safety line up the main rope in front of my ascenders!

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Team leaders, Julie Meachen, Xiaoming Wang, and Alan Cooper analyze the cave stratigraphy. Credit: L. Weyrich

The ascent took about 5 minutes, and was a stark reminder of how unfit I was. I was using a rope walking rig (3 points of contact, 1 free-floating on my right ankle) which was much faster than the simple frogging system the novices were going to use. Apart from the last section, the climb was a free-hang, with no wall to get in the way. The rigging was good, and the rope did not touch the wall (a major concern for abrasion) – so it was time to fetch Julie and Prof. Xiaoming Wang and return to the cave floor. Xiaoming was a graduate student at U Kansas in 1984 and participated in the last year of the excavations – so was an invaluable guide to what we were now looking at, and especially which areas of the cave had already been excavated. After we’d all descended into the cave, Xioaming was able to start comparing the original publications and records with what we could see 30 years later. His first task was to establish a grid of stringlines that would both guide our excavations, and enable them to be related to the original layout and materials from 1975-1984. While walking around he quickly spotted that one exposed slope of rock was full of horse bones, and a large unidentified vertebrae! We had our first Ice Age mammal – they were literally falling out of the walls.

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The first excavation team surveys the pit from the 1984 excavation, before laying down grid markings prior to excavation. Credit: L. Weyrich

The next day, we descended most of the paleontology team – and while there were a lot of nerves, everyone did well and there were no problems. Quickly, the nervous voices were replaced by exhilarated faces as the science team ran around identifying bones and marvelling at the scope of the deposit. We set to recovery operations for the exposed bones (or float) to prevent any further damage through unintentional trampling. Xiaoming and Steve finished the string grid overlying the full extent of the pit, allowing any bone to be placed precisely within space.

Packy Le Pue

Packy LePeu fell to his death during the excavations, and quickly became a morbid mascot, as animals that fall in the cave are quite slow to decompose. Credit: L. Weyrich

One of the packrats (quickly nicknamed Packy LePeu) must have tried a rope free descent during that first night, as we found him in the middle of the ‘drop zone’ of the cave floor – showing that NTC continues to add skeletons to its extensive collection. As Juan noted, it wasn’t the drop that killed Packy, but the rapid stop at the end. Such deep and poignant philosophy is rife in the caving community, and well worth noting.

Over the next few days, we divided up the teams to concentrate on excavating different fossiliferous ‘faces’ and to remove overburden to access new areas to prospect. We established plastic dropsheets against one wall, and dumped 5 gallon buckets of sediment and rocks in big piles. This enables the spoil to be easily identified in the future, and to be returned into excavated areas during backfilling. By the end of the week and a half operation, this pile stood about 5 ft high, 40 ft long, and 12 ft deep (1.5m x 15m x 4m) – which is an awful lot of heavy buckets carried around the dig and up the bank.

We soon started to find lots of large mammal bones, horses, mountain sheep, and then cheetah-like cats and wolves. Julie found a beautiful American lion tooth (a great big slicing molar), followed by another – and then with a loud cry ‘Holy shit,… I’ve got cat face!!!’ which apparently is what palaeontologists say when they find several front parts of a felid skull – but sounds more like a disease to me.

One thing that was quite evident though was that the original descriptions of the cave sediments, and the theories about how they had been deposited, looked quite inadequate. In my opinion, the depth of the sediments, and their remaining height on several walls, indicated that the deposit was originally much deeper and had been subsequently eroded (maybe during the Last Glacial Maximum, or the ensuing melting phase. The cave is situated just south of the leading edge of the Ice Sheets that covered southern Canada and the Pacific northwest – and was probably heavily impacted by the climate conditions they created). Looking around at the full cave deposit, I could only feel that we are looking at a former river system – in other words that the chamber was created when a large water course cut through the ridge, bringing with it large amounts of sediments and potentially also some bones. This is quite different to the original descriptions which suggested the deposits had all entered the cave through the current entrance!

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The American camel (Camelops hesternus) metatarsal bone is barely visible in the dirt before being removed from the dirt. Credit L. Weyrich

It was also quite obvious that the original descriptions of the stratigraphy (the layers and age of the sediments) were much too simplistic. A thick layer of ash (from some past eruption at Yellowstone) marked the top of a major infill event, which cut through the surrounding sediments and formed the top of a U/V shaped cross section. For any other fans of the much lamented Time Team (a pox on Channel 4 bureaucrats), as the great Phil says, ‘If it cuts through,… it must be younger’ … except with a much broader Wiltshire accent of course. Xiaoming was soon quite worried, as this infill was not shown on any of the original plans, yet appeared to cut right across the middle of the excavation. Furthermore, the complexity of down-cutting and infilling events, and the deeply sloping sedimentary layers, appeared much more complex than any of the publications. This suggested that we would not be able to use the original system of units and time periods that had been proposed, but would need to start building something again from scratch. To a degree that didn’t worry me, as I only really trust a carbon date on each bone I analyse – I have a healthy scepticism about using stratigraphic layers to provide age – particularly in caves, where every manner of geological event is compacted into a small 3-D space, and run at high speed. In a word, cave stratigraphy is normally a mess!

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Alan Cooper holds the rare find. Credit: L. Weyrich

I guess the highlight of that first week was pulling out some intact limb bones in good condition. One of the first was a beautiful camel metatarsal – or camel toe as I dubbed it – a huge bone. About 1 inch was showing in the midst of a compact layer of rocks and sediment, and as I was digging it out (with everyone watching) it just got longer and longer. First I thought it was a bison (due to the width of the end), then a horse (due to the length of the shaft vs the cross section) and then as the joints for the toes appeared – instantly I knew it was a Western Camel (Camelops hesternus) – a relatively rare find in such good condition. Great! Definitely one to sample for DNA and AMS….

One bizarre observation was that while most of the bones in the layers we examined were darkly stained, and relatively ‘rotten’ – likely to break easily, suggesting that the proteins/collagen had decayed, many had a tiny section of creamy white, ‘unaltered’ bone lining the marrow cavity. This crescent shaped layer, often only 1-2 mm thick, looked like fresh, unaltered bone and had ‘DNA here’ written all over it! I’ve never seen a similar situation before – normally when a bone is that far gone all of the bone is impacted. While the bone is still fine for morphological analyses (length, width, shape characteristics) the DNA has long gone – and indeed even radiocarbon dating may be difficult. Hence, the NTC material is most mysterious – and it will be very interesting to see what the DNA content will turn out to be. I want to get these samples processed in the next month to see what the answer is – so stay tuned! We’ll process the bone samples of the camel, bison, several horse species, the lion, American cheetah, wolves and mountain sheep – and sequence mitochondrial DNA as the first test. Details to follow….

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