Stop 9: Yosemite, Part 3

Updated 9/18/2014. I just realized that I had linked to the part 1 video and then the part 1 again.  Oops! The link is updated now and it should make a lot more sense!

Oh my, a three-part post about just one place?! Yes, Yosemite is a huge park with lots to see, and in our three days there, I feel like we only scratched the surface. At least we saw enough to know that there is much to do there, and we need to return.

On the morning of June 24th, we woke early, broke camp in Tuolumne Meadows and headed West and South toward Yosemite Valley. The drive was filled with ooohs and aaahs. We drove past El Capitan, then Half Dome. Yosemite Falls was flowing beautifully.

Yosemite falls

Having not been in Yosemite Valley before, I was a little surprised how many people (and cars!) were packed into the relatively narrow valley. The place bustled almost like a city. Between the valley walls were packed two roads (one Eastbound, one Westbound), some bike paths (a great way to relieve some of the road congestion), campgrounds (for those who book nearly a year in advance), lots of buses, the Merced River, Visitor Centers, in some areas a wide meadow, and lots of people. We knew Yosemite was a very popular summer destination, but driving and parking were a bit more complicated than I had planned. Still, the place seemed to run smoothly and we got to the Visitor Center almost on time. We had been given permission to park near the Visitor Center in an area designated for employees, which was nice. When we arrived we gathered our gear and headed right past the mule deer munching grass on the lawn of a chapel toward our meeting place.

Ranger Erik Westerlund was there to meet us. He said that he thought he’d walk us through his usual geology talk which he regularly presents to groups of visitors. We didn’t catch the beginning of the talk on video, so it starts off a little bit into the discussion. Ranger Erik is a biologist and always thought geology was boring, until two events changed his mind. I’ll let him tell the story. I will say it’s interesting to get two biologists together to talk about geology. He and I both kept interrupting the geologic story with “hey look, a Steller’s Jay!” and “is that milkweed?” and “how is the health of your monarch butterfly population?” I edited most of that out, but I might put together another video at the end with all the extraneous plant and animal talk. There are some really interesting stories in there! And besides, geology is Boring. Right?

Hey look, a Steller's Jay! (photo by Evan Kern)

And this is one of my favorite pics from the trip:

Showy milkweed and a bee (photo by Evan Kern)

I split the videos up in two so that they weren’t so hard to upload. Here is the first video. In this video, Ranger Erik explains how subduction of the Pacific oceanic plate under the North American plate along the coast of California caused the Sierra Nevada range to be uplifted. The Merced River cut the V-shaped Yosemite Valley. Then, much later, glaciers carved the valley. Since then, it has filled in with sediment to a very great thickness!

Before Erik explains why he finds geology interesting now, although he thought it was boring before, I think I should explain a few things.

Firstly, Erik talks about endemic species and endemism. I doubt my new students will know those words yet. Endemic species are species that only live in a certain area. We discussed the fact that California has a high degree of endemism, which means that there are many species that only live in California.

Secondly, I think a refresher on evolution is probably a good idea now. Erik finds geology interesting because in California, as in many places, geology has been a direct driver of evolution. There are several things people misunderstand about evolution, so let’s clear those up. First of all, individuals do not evolve; populations evolve. Secondly,evolution is simply a change in how common each genetic trait is in a population over time.For speciation (one population splitting into two species) to happen, there are certain criteria that must be met. Here is how a new species is formed: 1) The population must have some genetic diversity within it. If all the individuals within the population were the same, the population could not evolve. 2) Some members of the population have to be separated from other members for a long period of time (this is where the geology comes in). 3) In one of the two populations’ ecosystems (or in both), there has to be some environmental difference from the original populations’ ecosystem. It could be a climatic difference, it could be a different predator, or it could be a difference in vegetation. It could also be a social or behavioral difference. 4) In this new environment, some members of the population may have genetic differences that result in them being more successful at competing for resources (we call this “better adapted”) than other members. 5) As a result of this difference, the more successful ones will either have more offspring, or have more that survive. 6) The offspring will have the more successful traits passed on to them, so the more successful genes become more common within the population in the next generation. 7) Eventually, one population becomes so different from the other that they no longer can interbreed. They are now two different species.

So now, see if nunataks make sense as drivers of the evolution of the Lyell salamander!  (<– This is the link I messed up before.) I find it so interesting that California is a biodiversity hotspot, in part due to glaciers! Indiana had glaciers, too. Anyone want to guess why Indiana doesn’t have a high degree of endemism?


Black-headed Grosbeak (photo by Evan Kern)

Upon finishing the geology talk, we asked Erik for a recommendation on a trail. He suggested a hike up to Vernal Falls. We also got on the subject of food and he suggested Ramone’s Taco Truck. That is the beginning of another story that I will tell in the next post.

Bear trap

On the way to Vernal Falls, we saw some interesting things, including this bear trap in the campgrounds. I wondered how often it became a curious kid trap! Shortly after passing the bear trap, this little thing walked right past us along the sidewalk:

Young mule deer

At the trailhead, we enjoyed the view of the river:

The Merced River, below Vernal Falls

The trail to the falls is paved, popular, and a fairly steep up, up, up. There were lots of squirrels who were looking for some easy lunches in the form of handouts from hikers. They didn’t mind being petted at all. We didn’t pet or feed them for a couple of reasons… one because it is not good for them to become dependent on summer handouts, then have difficulty finding food for the winter, also because the little guys can carry fleas and diseases. Lots of other people enjoyed playing with them, though. I just enjoyed the fact that they seemed happy to model for my camera.

Not shy

Along the trail, there were a few places to stop and take some family portraits. One of my favorite things that happens along populated trails is the little interactions with other hikers. We offered to take a picture for a Japanese couple and their two little kids and they took a picture for us. This is one of the few “all four of us” pictures we got on the trip:

All four, near Vernal Falls

It wasn’t long before we were at the halfway point. We were tired and had a bit of a drive to Merced, CA that afternoon, so we decided not to go to the top. Here is the view of the falls from the bridge at the halfway point:

Vernal Falls

Once back in the valley, we hopped in the truck and headed off toward Merced, with visions of delicious taco truck burritos dancing in our heads.

Stop 9: Yosemite, part 2

On June 22nd, we got up and checked out a few places along the Tioga Road. After seeing giant sequoias in Tuolumne Grove, we went to find a couple of Earthcaches. If you’re not familiar with geocaching, check out this video. Geocaching involves finding hidden containers using a GPS, then signing the logbook inside and logging your find on the website. There is a special type of geocache designed to teach people about geology. These are called Earthcaches. The first was at Pothole Dome. Ranger Erik is going to explain the geology of Yosemite in the next video, but a short explanation would be useful here. The main rock you see in Yosemite is granite. Granite is an intrusive igneous rock, so it was pushed up under the overlying rock. The overlying rock has been eroded away since. After that, Yosemite had many glaciers which further sculpted the rock.The Pothole Dome Earthcache would teach us about how glaciers leave their mark on granite.

Getting there

To get to Pothole Dome, we followed the trail along the edge of Tuolumne Meadow.

Stay on the trail!

When we got to the bottom of the dome, we realized we needed to climb up. Luckily the granite is great to climb, and parts of the dome aren’t steep. We had a nice little walk up.

Walking up Pothole Dome

Partway up I stopped to snap some pictures of the incredible view:

The Meadow from the Dome

We finally stopped at the location of the cache. We were asked to find evidence of glaciers. I’m not going to give away the answers to the cache, but I’ll tell you what we learned. First, we learned to find “glacial polish”. Just as it sounds, glacial polish is parts of rock that have been polished by a glacier sliding over the top of the rock. I took a few pictures of this phenomenon, but this one is my favorite:

Glacial Polish

Within the polish, it is possible to see striations where rocks were embedded in the glacier and scraped into the granite. This shows which direction the glacier was moving!

We also looked at “glacial erratics”, which are large rocks that were carried by the glacier from a different area, then dropped as the glacier melted and receded. You can tell these boulders (below) do not have the same composition as Pothole Dome by comparing their colors to those shown above.


The boys thought the erratics were good for climbing, not just for educating us about where the glaciers came from.

Erratics are fun

We also noticed that you could even see that the glaciers were up pretty high (but not all the way up) on the mountains.

Can you tell where the glaciers stopped?

We also noticed lines of different material in the dome. Ranger Erik later explained that this is called a dike. It happened when the granite cooled and cracked, then another mineral with a lower freezing point oozed into the cracks and filled them.

A dike

We noticed in some places that plants found the dikes useful. The rock that filled this crack must have been softer than the surrounding rock. This is why I love earthcaches… I just heard from the cacher who owns this one. He is a geologist, and suggested that I was mistaken here. His explanation for the trees growing here is a joint, not a dike. Dikes (including the one we saw above) are generally made of harder minerals than the surrounding rock and erode more slowly, so they tend to stick up from the rock. Obviously, the one below is a low spot. It makes more sense that this is a joint that has been filled in with loose sediment, making enough of a soil for the trees to be able to exploit this spot! (For the record, I’m leaving my previous comments because I think the learning process is interesting here. I’m enjoying the willingness of so many people to help me get a better understanding of all this!)

Trees growing in a joint.

After finding the answers to our cache questions, we headed back down. Evan and Kieran jumped or climbed on just about every erratic they encountered and I took pictures of rocks and flowers. Here is a video David took from the top of Pothole Dome.

These flowers grew along roadsides and on the dome.

We decided to go back to camp for a little while to catch our breath, then drove out to find another earthcache near sunset. This was another one that teaches about glacial geology… potholes this time. We had seen some potholes on Pothole Dome, but they weren’t as prominent as the ones we saw near the Tuolumne River.

Tuolumne River

Potholes are formed when a rock falls into a small depression where water is washing over it. The rock gets pushed around in the depression, and scrapes rock out of the walls. Here is the best example of a pothole we saw:

A pothole

After finding the cache, we stopped along the river in another place and found even more potholes!

More potholes!

We loved being near the river and got lots of great pictures as the sun was setting. Here is a video David took of the river.

Tuolumne River

I love pictures of trails. They always make me want to get out there and have a new adventure.

The trail beckons

After our lovely little walk by the river, we went back to camp and enjoyed a cool evening around the fire. We had to be up early the next morning to meet with a ranger in Yosemite Valley, and it was an hour drive away. Between that and having to pack up the campsite in the morning, you would think we would have gone to bed early. But the stars were so beautiful and the fire was so warm, we stayed up longer than we should have. We had no intention of missing any of the beauty of Yosemite that night.