37°50'42"N 119°29'26"W

Magmatic FeatureS:

Dikes

In Yosemite, we can often see many rocks that look like the examples below:

37°48'24"N 119°32'43"W

Notice in these pictures that there is a stripe on the rock that is a different color than the surrounding rock. These peculiar stripes in the rock are magmatic structures called dikes.

Watch the video below to learn about what dikes are and how they form!

37°52'39"N 119°23'34"W

Let's think about how this magma moves! Once the fissure is created in the rock, magma moves through it, causing the crack to expand and allow more magma to flow. When this magma is moving through this rock, its pressure forces the existing rock to expand outward. Observe this quick video below to understand why rocks separate as magma moves through it.

Just like these pens (representing magma) pushed aside the marbles (representing rock) as they moved through them, magma pushes aside rock as it moves through it! This is important to remember when thinking about relative dating.

According to the Law of Cross-Cutting Relationships, the dike must be younger than the rock it is surrounded by because the rock had to have existed first in order for the magma to have moved through it.

Let's look at some examples of dikes in Yosemite! Dikes can come in many different sizes, colors, and textures.