Pothole Dome

Pothole Dome is a granite dome in Yosemite right off the Tioga road, that has an abundance of geologic features showing the effects of glaciers and water under pressure.

Pothole Dome is located in Tuolumne Meadows. If you’re driving from the west it’s the first dome on your left as you enter The Meadows. It’s a short and small little dome, and is an easy climb for families.

The first clue that glaciers have been here is the shape of Pothole Dome. The steep west side and gradually sloping east side is evidence that glaciers flowed from the east to the west over Pothole Dome, smoothing out the east side as the ice rose up over the dome, and steepening the west side as the glacier plucked rock off as it passed. This shape, called a roche moutonnee, is french for sheep back, and is common in highly glaciated areas.

As you approach Pothole dome, the trail takes you along the side of the dome to the east side that has a more gentle slope, but if you take a quick walk to the steep side you can see the many rocks and boulders that have been broken off the steep side as water and ice flowed off the glacier loosening the rock as water froze and melted. There is also amazing scalloping of the rock where it looks like scoops have been carved out of the rock. Scallops are created by water flow, similar to the waves created in the sand at a beach or ripples at the bottom of a river. To create scallops in granite though requires tremendous pressure along with abrasives such as silt, sand, and rock. The glacier that traveled over pothole dome was up to 2000 ft. thick, providiing the pressure, water, and abrasives to cause this scalloping.

About half way up the trail if you keep your eye out for some trees up on the dome and move off trail onto the dome, you will come to the reason Pothole Dome got it’s name, Potholes.

Potholes are large holes in the granite that are shaped like big pots. Potholes are formed when water and and boulders under pressure churned around and around like a washing machine in the hole, The polished boulders, called grinders, can still be found in some of the potholes, but most have filled with dirt and trees are growing out of them.

As you start your climb of Pothole dome you will come to many polished surfaces where the glacier shined the granite as it flowed up and across the surface. A close inspection shows lines in the direction the glacier was moving.

Also near the bottom are chatter marks, where boulders carried along in the ice bumped up against pothole dome as they moved up the slope. finding these chatter marks is a challenge but take the time to look around near the bottom of the dome. Finding these features can be an exciting challenge for kids.

Moving further up the slope one can find long lines of crystal in the granite. These are called dykes, formed when magma rose up through cracks in the already solidified granite and cooled. The dyke is MADE OF stronger material than the granite, so the granite has been weathered away while the dyke has not.

Pothole dome is made of cathedral peak granodiorite, a distinctive granite that contains large crystals, called phenocrysts. Some of the boulders on top of pothole dome are not the same type of granite. These are called glacial erratics. They were brought here from far away by the glacier. When the glacier melted fifteen thousand years ago, the boulders dropped where they sit now.

Pothole dome is a small unassuming granite hill right near Tioga road with thousands of amazing features just waiting for you to find.  Go climb a rock.

As you walk along the side of Pothole dome, look further up and you will see more scalloped surfaces.

Things to shoot: Potholes, scalloped surfaces, flutes, striations, chattermarks, flutes and striations showing water flowing up and ice to the side.

These related granitic rocks, referred to as the Tuolumne Intrusive Suite, were intruded into the Sierra Nevada batholith during Cretaceous time, about 86 to 91 million years ago. 

These related granitic rocks, referred to as the Tuolumne Intrusive Suite, were intruded into the Sierra Nevada batholith during Cretaceous time, about 86 to 91 million years ago. 

The next rock to crystallize was the Cathedral Peak Granodiorite. This rock is readily identified by its large phenocrysts of potassium feldspar, and forms most of the core of the pluton. The Cathedral Peak Granodiorite is very widespread in Tuolumne Meadows and there are excellent exposures of these rocks at Lembert Dome and Pothole Dome. 

During the last glacial episode, Tuolumne Meadows was covered by the 2,000-foot thick Tuolumne icefield 

The spinning rocks, called grinders, drill holes into the rock by abrasion.