Saturday, February 27, 2016

Ancient Lakes

Dusty Lake in Potholes Coulee
7.2 miles loop, 800 feet elevation gain
Difficulty: Easy-moderate
Access: Washington State Parks Discovery Pass required ($10/day, $30/annual); trailhead at the end of a good gravel road

Washington State's Columbia Plateau can seem largely featureless and drab for drivers traveling through the region along I-90, but just a few miles off the interstate lie some fascinating landscapes shaped by the many violent geological phenomena. Hidden among the desert and reclaimed farmland of Eastern Washington lie dramatic coulees cut into cliffs of columnar basalt. Nowhere is this landscape more beautiful and easily explored than at Potholes Coulee with the hike to Ancient Lakes, just southwest of Quincy. On the dry side of the Cascades, Ancient Lakes usually stays at least somewhat sunny when winter rains drench Seattle. The hike itself is generally easy and flat and recommended to anyone in the area with a few spare hours, as well to Seattle residents hoping to rediscover the sun during the drabbest, stormiest days of the year.

I headed to Ancient Lakes with two friends from Seattle on a rainy Sunday. We followed I-90 west for two hours past Snoqualmie Pass, Ellensburg, and Vantage to George, where we exited the interstate at Exit 149 and followed Route 281 north. We followed 281 through the farmland of the Quincy Basin to the junction with White Trail Road; we turned left onto White Trail Road and followed it around a wide bend to the right until we reached Road 9; we turned left onto Road 9 and followed it downhill past views of the Columbia River and its beautiful gorge all until it turned into a gravel road; we continued on the gravel road until it dead-ended at the trailhead for Ancient Lakes, where a sign indicated that we should display a Discover Pass.

The trail was simply a continuation of the gravel road. We followed the wide gravel path south through the sagebrush, following the base of the a set of columnar basalt cliffs that rose prominently to the east. About half of a mile in, the cliffs to the east opened up to expose Potholes Coulee, a wide canyon filled with shrubs cut into the surrounding basalt landscape. We skipped the initial path leading left into the coulee but took the second, narrower trail that branched off to the left. There were numerous use trails in the coulee that split apart or came back together; it was difficult to keep track of which exact path we were on. However, for the most part, this mattered little; we followed the general direction of hiking deeper into the coulee.

The layers of regularly shaped hexagonal columnar basalt that formed the walls of the coulee were the result of massive volcano eruptions in what is now the Pacific Northwest around 15 million years ago. These eruptions differed greatly from the eruptions that formed the modern Cascade stratovolcanoes; instead, the ancient eruptions occurred in the form of flood basalts, in which lava emerging from the volcanic source covered the entire Columbia River Basin, forming the Columbia River Flood Basalts. Multiple eruptions from this source led to many layers of flood basalts, each set atop the previous eruption's layer. Quickly cooling mafic lava, such as that found in the Columbia River Flood Basalt eruptions, contracts to form joints between sections of exposed lava, eventually forming the vertical columns so commonly seen in Eastern Washington. The source of these massive flood basalts that covered much of the Eastern Washington and Oregon is still disputed; one suggestion is that the basalts formed from an earlier manifestation of the Yellowstone Hot Spot, which may have later migrated across Idaho to form the Snake River Plain as the North American Plate moved before reaching its current position beneath the hot springs in Wyoming.

Potholes Coulee
We followed the flat trail through the coulee, hiking through the sage and the tumbleweed under the cliffs of columnar basalt that flanked us to the left. About a mile after turning into the coulee, we came to a small waterfall that tumbled off the north wall of the coulee, a pretty drop without much flow.

Waterfall in Potholes Coulee
Hiking further down the coulee, we came to the first of the four lakes in the coulee. This smallest of the lakes was ringed by trees and denser brush and was at least temporary home to a sizable flock of waterfowl. The uneven, jagged walls of the ridge separating the two halfs of Potholes Coulee rose behind the lake, an oddly juxtaposed sight of brush, water, and basalt.

First pond in the coulee
Just further down the trail, we came to three more lakes. The first of the three was large and more oblong; the remaining pair were separated by a flat, defined grassy ridge. The walls of the coulee closed behind these last two lakes, with a waterfall plunging from the land above the coulee into the northeastern lake. While the landscape seemed remote and almost prehistoric, we were reminded at times of our proximity to civilization by the power lines we could sometimes see running across the flat Columbia Plateau above the coulee.

Ancient Lakes
We saw a group camping along the ridge between the easternmost two lakes in the coulee, so rather than heading onto that ridge we chose to hike around the northeastern lake to reach the waterfall at the head of the coulee. We followed the west and north shores of that lake towards the waterfall, with good views of the lake and reflections of the surrounding basalt cliffs. The north shore of the lake was formed by a talus slope of crumbling fragments of the basalt cliffs, so we had to scramble over sections of the talus to reach the waterfall at the end of the lake. Along the way, one of my friends discovered that flattened shards of basalt made for decent skipping stones, so we stopped in the talus to skip rocks into the waters of the Ancient Lakes.

Ancient Lakes
At the end of the talus slope, we found a slightly flatter area with more solid ground at the foot of the waterfall, which made a pretty plunge down the basalt layers of the Columbia Plateau. Unfortunately, some rocks in the area had been vandalized, with graffiti decorating what would otherwise have felt like a remote and almost unspoiled place.

Waterfall at the head of the coulee
Tens of thousands of years ago, a much larger waterfall cut into the head of Potholes Coulee: in fact, it is likely that the entire head of the coulee was filled with falling floodwaters. While the basalt cliffs of Potholes Coulee were formed by the fiery outpouring of molten rock from the earth, the actual coulees themselves were carved out by cataclysmic floods of unimaginable volume and power. These floods were released by the draining of glacial Lake Missoula during recent ice ages. Glaciers in the Rocky Mountains dammed what is today the Clark Fork of the Columbia, creating a lake nearly four times the volume of modern Lake Erie. At times, the glacial dam that held back the lake would break apart, causing a sudden release of water across the Columbia Plateau with a flow rate more than tenfold that of the Amazon River. Floodwaters scoured the flat desert landscape and carved numerous channels through the Columbia Plateau, including Potholes Coulee. The block-like nature of the columnar basalt walls caused the columns to come off one by one or in blocks, forming coulees with nearly vertical walls.

It took geologists a long time to come with grips with the idea that the desert coulees of the Columbia Plateau were carved out by massive Ice Age floods. After all, modern geology was born with James Hutton's principle of uniformitarianism- the idea that geological processes occuring today are the same as ones that have occurred in the past. Geologist J Harlan Bretz first hypothesized that the coulees and the Channeled Scablands of the Columbia Plateau were formed by massive floods, but was written off by more established geologists as a lunatic, a fool, or an amateur. If massive, catastrophic floods of the scale Bretz proposed never occur today, they reasoned, why and how would they have occurred in the past? Yet increasing evidence pointed to the validity of Bretz's theory: both the head of Potholes Coulees and Dry Falls on the Grand Coulee showed signs of having been ancient waterfalls and the discovery of a "bathtub ring" along the mountains above the Clark Fork in Idaho and Montana validated the existence of glacial Lake Missoula. Today, the combined effects of the Columbia Plateau flood basalts and the the Missoula floods on this landscape make it one of the most geologically fascinating areas in the country.

The waterfall that today flows down the head of Potholes Coulee is fed by a non-natural source: it is only a year-round waterfall because of irrigation runoff from the Bureau of Reclamation's Columbia Basin Project. The Columbia Plateau is a desert with just enough water to support sagebrush and tumbleweed, but the Columbia Basin Project turned the area into farmland. A massive works project during the Great Depression led to the construction of the Grand Coulee Dam on the Columbia River. Today, river water is stored in Banks Lake and reaches farms near Quincy, Ephrata, and Moses Lake through irrigation canals, allowing for agriculture in an arid land. The agricultural benefits are clearly great, but the price tag of the project and the environmental consequences on water quality and Columbia River salmon populations have perhaps been equally large.

After lunch at the foot of the waterfall, we retraced our steps along the lakeshore back to the ridge separating the three lakes. From the ridge, we followed a trail that traced the west lakeshore of the southeastern lake, which had a particularly round and pleasant shape. We followed the trail past the lake and briefly uphill and found an unmarked trail heading off towards the left. At this junction, we decided to check out what we would find on the spur and left the wider main trail.

The spur began the first steeper climb of the hike; we soon realized it wasn't actually a spur trail but instead a longer trail that followed one of the higher benches on the coulee. We found a small cave to the right of this trail: the cave wasn't deep but allowed us to explore a small basalt overhang that must have been carved out by the Missoula Floods. Inside the cave, we could clearly make out the polygonal shapes of the basalt columns.

Cave in the basalt
Across the trail from the cave, there was a good view of all three Ancient Lakes and of the north wall of Potholes Coulees.

Ancient Lakes
The trail continued onwards towards the base of a set of basalt cliffs, then curved to the right and followed the foot of those cliffs for the next half mile or so. We passed by one unmarked trail that led off to the left at a break in the cliffs; after checking Google Maps afterwards, it appeared that this trail led up and out of the coulee to the roads and farmland above. We then came to a second junction with a trail heading off to the left towards a notch in the basalt cliffs. We took this left fork and followed the trail steeply up through basalt talus to the notch itself, where we found an incredible view into the other half of Potholes Coulee. Dusty Lake filled this half of the coulee and was much larger than any of the lakes we had seen earlier. From this pass, the basalt columns appeared at eye level. The line of basalt columns forming the cliffs on either side of the notch made for a striking scene. The opposite wall of the coulee was a solid line of cliffs; above the cliffs, we could see the neat rows of fruit trees of Columbia Basin Project farmland. We saw a hiker use this notch as a pass between the two halves of the coulee, following a trail that ran along the base of the upper cliffs before descending to Dusty Lake. We chose to stay on the Ancient Lakes side of the coulee as the hike out from Dusty Lake appeared to involve a decent amount of scrambling.

Looking towards Dusty Lake from Potholes Coulee pass
We returned from the pass to the upper trail along the high bench on the south side of Potholes Coulee. Continuing west along that trail, we soon came to another left fork leading to yet another notch. We decided to explore this spur trail as well and were glad we did. The short spur led very quickly uphill through loose talus up to the notch, where there were simultaneous views of both halves of the coulee and of all of the lakes in both halves of the coulee. Even more impressive were the well-defined basalt columns just to the right of the notch. A path led up from the notch onto the top of the ridgeline itself, providing sweeping views of the coulees and a close look at the hexagonal columnar basalt. I've never seen columnar basalt anywhere else as impressive, close-up, and well-defined as I did along the clifftops at Potholes Coulee; Shenandoah's Compton Peak got nothing on these basalts.

Columnar basalt in Potholes Coulee
We followed another use path from the ridgeline back to the upper bench trail. Immediately after returning to the bench trail, that trail began to descend off the upper bench and back to the floor of the coulee. The path made a steep and quick descent through the talus back to the valley floor. We followed the left fork at the base of the talus to head west out of the coulee. By this time, the sun had just set and the cloudy skies were beginning to darken, so we made our way quickly along the trail all the way west until we met exited the coulee and met up with the initial wide gravel road trail from which we had come; we turned right at the trail and followed it north back to the trailhead. We made the drive back to Seattle over Snoqualmie Pass in the dark and arrived back in the Sound area early enough to grab dinner at Chaat House in Bellevue.

The landscape of Potholes Coulee is remarkable and geologically fascinating. While many hikers may prefer to stay in the Cascades to enjoy Washington's alpine terrain, I found the desert to be equally interesting and enjoyable, if in different ways. Don't write off the desert: go and explore this terrain of eroded basalts and lakes.

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