It is not unusual for a tree to sprout on a bolder. To calculate the age of this struggling fir tree, simply count the swirls. Each year a fir tree will sprout a new ring of evenly spaced branches that circle the crown. Each ring is called a swirl. Using that method this tree was probably born in 19–. This is not the first tree to colonize this bolder. If the life expectancy of a tree trying to survive on the rock surface is no more than 30 years, there could have been several hundred trees that preceded this one.

A close examination shows how the forces of rain, wind, freezing, and biology are slowly eroding it. The tiny grains that get dislodged from the bolder and washed into the soil contribute minerals to the soil. This bolder was significantly larger. Based on the climate and other factors, a good estimate is that erosion will remove about 1 inch and about 8 gallons of material every 500 years. Projecting that rate over 12,000 years that this bolder has been sitting here, two feet of its surface has disappeared, while about 190 gallons of material have dissolved into the soil. In about 20,000 years from now, at this rate, it will be completely gone.

All the glacial erratics here have also experienced that magnitude of shrinkage. Since the eroding forces strike them evenly across their surfaces, it also tends to sculpt the boulders into the smooth spherical shapes you see.

As you study the boulder, you may draw other conclusions. We welcome your opinions and observations. You can contribute them below.