WATCHING FOR ROCKS Travels of a Sharp-Eyed Geologist

Time flies! The end of my summer season at Yellowstone is a mere four days away. Today was my final morning working the visitor center desk at Grant Village. It was my final afternoon leading a guided walk around West Thumb Geyser Basin. I’ll have tomorrow to tidy up any seasonal loose ends. On Friday I’ll pack my car and then on Saturday/Sunday I’ll be on a last weekend hike to Shoshone Lake with my backpacking co–workers. On Monday I’ll drive away to Salt Lake City for a visit with my nephew.
Sadly, I’ve got to relinquish my actually–not–so–bad–and–kinda–cozy government housing unit where I’ve lived since May 13. I’ve got to abandon listening to the eerie sounds of elk bugling in the early hours of these crisp autumn mornings. And worst of all, I’ve got to return the lovely geologic map of Yellowstone that I’ve diligently attempted to wrap my mind around pretty much each and every day of the past four months.
Along with 144 pages of accompanying text, the map has helped me on my lengthy journey of figuring out at least some of the rock formations in the park. The map belongs with the Grant Village library and must stay here, tucked into its own personal shelf space during the long, cold northwestern Wyoming winter. I asked the map if perhaps it wanted to spend the next few months with me in sunny southern Utah, but it declined graciously. It knows where its home is. To me, the rocks of Yellowstone are a confusing mish–mash of volcanic mush. Rhyolite! Welded tuff! Lava flows! I know what these words mean, but it’s not been easy to wrap my mind around what I see on the ground.

Madison River cutting through rhyolite and basalt flows of the caldera

I’ve had a wonderful summer trying to figure it all out, though.
This evening the interpretive staff got together for wine, cheese, fruit, and dessert. Awards were given out by our supervisor. For my continual efforts to construct a workable exploding caldera with balloons, a juice bottle, baking soda, vinegar, dish soap, and a drip pan from an electric stove (not to mention several rolls of aluminum foil), I was awarded the “Explosive Mad Science”  certificate. I was surprised and pleased to also be awarded the seasonal Ranger Safety Award – but not, remarkably, for my exploding caldera efforts. I thanked my Friday–hiking, bicycle–riding, beer–drinking buddy Sacha for all the fun we had together this summer. It helped that she honestly does hike as slowly as I do!

IMG_9167Sacha AfterHeartLake Backpack
Sacha sure could use some Jiffy Pop!


IMG_9176LastDay AtTheDesk
Last day at the desk


     IMG_9190West ThumbGeyser Basin
West Thumb Geyser Basin – my summer office

Upon consideration, you might think that with a name like Harlequin Lake there would at least be some harlequin ducks floating around. Au contraire, my friends! Harlequin Lake, situated inside Yellowstone National Park between Madison and West Yellowstone, is not known for its ducks. It is, however, known for two other notable features:
1) a lava flow2) beavers
This particular lava flow is not any ordinary lava flow. It has a remarkable reversepaleomagnetic polarity. Approximately every 200,000 to 300,000 years the magnetic polarity of the Earth flips. These links to web sites of PBS Nova and the British Geologic Survey each offer a fine explanation of this phenomenon. And beavers are truly among the most astounding of Earth’s engineers, whether two-footed or four. I simply had to go there!

IMG_8924 HarlequinLake
Harlequin Lake

Without getting deep into something I know next to nothing about, I will say that as molten lava flows and cools and solidifies, any iron-bearing minerals in it (such as hematite) adjust themselves according to the Earth’s magnetic North-South orientation of the day. What is so interesting about the Harlequin Lake flow, which occurred around 840,000 years ago, is that, at the time the flow occurred, North was apparently South and South was apparently North. If you had stood there with a compass, the needle would have pointed South instead of North.
According to Christiansen (2001), the Mount Jackson Rhyolite is a sequence of eight lava flows at the beginning of the third and most recent volcanic cycle of the Yellowstone hot spot. The Harlequin Lake flow occurred during this sequence.
So the other day I dragged Friday–hiking–buddy Sacha out with me, to see what we could see. We each had a compass, the better to investigate this remnant magnetism. We wanted to find out for ourselves if the needle would indeed deflect South. A perusal of any beaver activity in the area was also on the agenda.

IMG_8938ShouldBeThe HarlequinLakeFlow
Alleged Harlequin Lake flow
IMG_8919Sacha_ Compass_AndThe Hill
Looking for North

At the trail head parking lot I looked at the geologic map for the zillionth time. I stared intently at the hill across the highway. This had to be the right place. The hillside, however, was dense and impenetrable with a 23–year old lodgepole pine forest, sprouted after the 1988 fires. I knew that lodgepole cones could drop 10,000 seeds per acre after a fire and this hill looked to me like every single one of them had taken firm root. We decided to check out the beaver situation first and then attack the hill on the way out. It would have been really nice to spot a beaver or two in action, slapping mud onto newly–arranged lodge logs with their flat fat tails, but since they are crepuscular little critters, and it being around noon, we were not really surprised that we didn’t see them. What we did see, though, were half a dozen lodges scattered about at intervals on the far side of the lake. We also noticed that a considerable portion of the forest edging the lake had succumbed to the beaver’s incessant appetite.

IMG_8934Beaver Lodge_Harlequin Lake
Beaver lodge on Harlequin Lake


IMG_8929Beaver Lodge_Harlequin Lake
A marvel of engineering


IMG_8932Beavers BeenHere
Beavers been here!

I’m not sure what fascinates me so about beavers, but I do a short ranger program on them once a week and have learned some amazing beaver facts. They mate for life, are driven by the sound of running water to build dams and lodges that are marvels of engineering, can swim underwater for ½ mile and remain underwater for up to 15 minutes, can gnaw a 5–inch diameter tree in three minutes, and have two sets of lips! Yes, it’s true. Not one person I have spoken with knows this fact about beaver lips. If you think about it, two sets of lips make perfect sense. Beavers often gnaw trees beneath the water of lakes and ponds – the set of lips behind their teeth remain closed while they chomp on the tree. When they are ready to swallow that tasty bit of willow or aspen, the lips in front of their teeth close and the inside lips open, allowing the beaver to swallow. After our foray into all things beaver we decided we could not let a bunch of trees hinder us from discovering all things paleomagnetic. We proceeded to thrash our way loudly up the hill to a large outcrop, placing our compasses directly on various rocks along the way.

IMG_8935Needle PointingNorth
On the rocks


IMG_8936 MountHaynes
Mt. Haynes

I was positive we were right on the Harlequin Lake flow and that we would soon see the compass needle quiver and zip around to point towards Mt. Haynes towards the South. I’ve seen this phenomenon in southern Utah. In the Condor Canyon Formation there is a layer of ash called the Swett Tuff member. If you happen to find yourself standing, say, 20 yards or more away from this Swett Tuff while holding a good compass, the needle will point north as expected. But move ever so slowly closer and closer to the Swett Tuff and your compass needle will start to quiver. Keep moving closer, and closer, and closer until you are within inches of the tuff at which point your compass needle will have flipped. Your compass needle will now be pointing to the south. Dang! We poked around for 45 minutes or so, placing the compasses here and there directly on the rhyolite. But much to our dismay our compass needles never did deflect to the south. Why? I have no idea. According to my geologic map we were in the right place.
The next time I go searching for reverse paleomagnetic polarity, I will definitely walk every square inch of that hill. Perhaps I can first hire a beaver to gnaw down all the trees, too.
*************Reference:Christiansen, R.L., 2001, The Quaternary and Pliocene Yellowstone Plateau Volcanic Field of Wyoming, Idaho, and Montana, USGS Professional Paper 729-G.

IMG_8967 HarlequinLakeArea
Pencil points to Qml = Harlequin Lake flow

This summer, quite a few visitors to Yellowstone have walked up to the Grant Village visitor center desk and asked me the same question. “Can you tell me what your favorite hike is? I know you’ve got to have one that you like the best.” The implication is that they would go ahead and hike that particular trail since it is a ranger’s favorite. Well, besides reminding them that my personal choice might not necessarily coincide with their personal choice, I would always respond by saying that all the trails I’d hiked so far are equally my favorites.
Until yesterday.

IMG_8869Gallatin Range FromObservation Peak
Gallatin Range from Observation Peak

I can’t even really be certain what it is about Observation Peak that catapulted it to the top of my Favorite Yellowstone Hikes list. There are more than 1,000 miles of trails in Yellowstone, and I’ve hiked maybe 80 or so of them during the course of this summer. All of the trails I’ve traversed are distinctive and absolutely exquisite. And so I’ve got at least 900 more miles of trails to hike before I need to repeat any! But Observation Peak is without doubt a special place. I will definitely go again sooner than later.
Friday–hiking buddy Sasha and I chose to start our trek one mile north of Canyon junction on the Canyon–Tower Road. After a brief foray through a pine forest we soon broke out into open meadows and across small spring creeks for 2.2 miles to Cascade Lake, a small lake situated on the Solfatara Plateau at the base of the Washburn Range.

IMG_8830On CascadeLake Trail
Yours Truly
IMG_8834Hiking Buddy_Sasha
Sasha points the way
Cascade Lake trail on the Solfatara Plateau

A few bison were grazing at the far end of the meadows, too distant even in their enormity for any great photo opportunity. Fireweed ablaze in rusty red–orange hues told us that the brief Yellowstone summer is nearly over in this mountainous plateau country of northwestern Wyoming. A pair of swans (trumpeter? tundra?) were busily feeding near the lake edge, their sleek curved necks bobbing and dipping underwater until only their rounded white posteriors were visible. Here a sign directed us to the next segment of the trail, away from the easier level walking of the meadows to start our assault the mountain.

IMG_8907SwanAt CascadeLake IMG_8843Swan Feeding

We would climb 1400 feet in the next three miles and be rewarded with dazzling views of Grebe Lake (headwaters of the Gibbon River, which joins the Firehole River at Madison to become the Madison River), Hayden Valley, and the Central Plateau of the Yellowstone caldera. Entire hillsides, now recovering, were burned in the fires of 1988 that swept through 793,000 acres – about 36% of the park. Every summer fires occur; the hazy sky in these images is caused by the Point fire on the east side of Yellowstone Lake.

IMG_8881Gibbon RiverFlowingFromGrebeLake
Grebe Lake, the headwaters of Gibbon River

Of the two main episodes of volcanism in the Yellowstone area, the Washburn Range Volcano in the north–central part of the park came into existence during an older period of volcanic activity that occurred in northwestern Wyoming 55–40 million years ago during the Eocene epoch. During this tectonically active time other volcanic fields were also formed – the Absaroka Range along the eastern side of the park, Bunsen Peak south of Mammoth Hot Springs in the northern part of the park, and intrusive igneous rocks of the southern Gallatin Range in the northwestern corner of the park.
Since Observation Peak is part of the Washburn Range I expected to see similar kinds of rocks that are on Mt. Washburn to the east. I also checked the geologic map. As we gained elevation I ooohed and aaahed at outcrops of angular conglomerate or breccia – coarse, angular fragments of rock in a fine-grained matrix – indicating past mudflows and debris flows from Eocene volcanic activity.

IMG_8847Breccia Outcrop


IMG_8862Breccia Outcrop_SashaForScale
Breccia outcrop – Sasha for scale


Vein of opalized silica

But at the peak, the rock seemed to change from this breccia; the peak appears to have been mapped as part of the Pleistocene Swan Lake Flow basalt. This basalt flow would have occurred after the third caldera-forming eruption of 640,000 years ago. Since Observation Peak itself is outside of the caldera boundary its rocks would not have been obliterated by the explosion. However, lava flows such as the Swan Lake Flow, which occurred for hundreds of thousands of years after the caldera–forming explosions, could naturally have blanketed these nearby older rocks of the Washburn Range.
I could be mistaken about the Swan Lake Flow being at the top of Observation Peak, however – it is mapped as a tiny speck within the Tertiary volcanics and I could be looking at the wrong contour. The rocks on the peak looked less to me like a basalt than a tuff, but they were definitely not breccia. Unfortunately the trail is not drawn to the peak on the geologic map but follows away from it, around Cascade Lake to Grebe Lake. For me, fine-grained volcanic rocks can be difficult to identify in the field.

IMG_8880Grebe LakeAndThe CentralPlateau
Grebe Lake and the Central Plateau

We stopped to watch a pair of blue grouse clucking in the undergrowth. On our return trip down past Cascade Lake the two swans were still busily feeding, but in the meadows the bison were nowhere to be seen. The guidebook says that in years past there has been a beaver lodge at the south end of the lake and a lodge and dam on Cascade Creek. When I return next time I will most certainly check them out.

IMG_8889Blue Grouse
Blue grouse


IMG_8892Blue Grouse
Blue grouse
Fireweed of late summer


 Check it out
Christiansen, R.L., 2001, The Quaternary and Pliocene Yellowstone Plateau Volcanic Field of Wyoming, Idaho, and Montana, USGS Professional Paper 729-G.
Marschall, M.C. & Marschall, J.S., 2008, Yellowstone Trails: A Hiking Guide, 30th Anniversary Edition, Yellowstone Association.

Working as a seasonal interpretive ranger at Yellowstone, I get asked a lot of the same questions over and over. One of the most frequent inquiries (besides “What is there to do in Yellowstone?”) concerns Grand Teton National Park, just to the south.
“We’re going to Grand Teton after Yellowstone. What’s there?”

And so, if they seem interested, I spend some time trying to explain a bit about the geology. You see, I say, there is this mountain range that was thrust upward over at least the past 13  million years along a major fault…and a river that flows south from Yellowstone and west from the continental divide and ultimately into the Pacific Ocean…and U-shaped valleys as evidence of recent glaciers…

You really just have to see it.

IMG_6551Snake RiverAndTeton Range InJacksonWY
Snake River and Teton Range at Jackson, Wyoming


IMG_6553Teton RangeFrom JacksonHoleWY
Teton Range from Jackson Hole, Wyoming


IMG_6569Snake RiverAndTeton Range
 Snake River flowing south into Grand Teton National Park
IMG_7931Snake RiverAnd GrandTeton
 Teton Range from Snake River Overlook
Moonset over Teton Range