Just at the north entrance to South Seattle College on 16th SW sits a massive rock that is hard to ignore. How does a rock like that get there? It looks to be an estimated 9 feet tall, 13 feet wide and 20 feet long. Rocks like that however are surprisingly common. How did they get where they are? Glaciers.

The Washington Department of Natural Resources explains that roughly 17,000 years ago an extension of what was called the Cordilleran Ice Sheet, known as the Puget Lobe covered the entire Puget Sound region. That glacier advanced and retreated over time and as it did, transient glacial lakes were formed. As the ice retreated different spillways were created for the water to escape.

"The Vashon Stade, part of the Fraser Glaciation was the latest major incursion of ice into the Puget Lowland. Ice advance as south as Tenino, WA, and was upward of 4,200 feet thick in the northern Puget Lowland.

As the ice retreated, rocks like that called Glacial Erratic Boulders were moved into King County

 

According to Nick Zentner of Central Washington University Department of Geological Sciences,

"Canadian rocks are strewn all over the Puget lowland, stretching from the Olympic Peninsula clear over to the Cascade Range." 

Erratics can be found at altitudes up to about 1,300–1,600 feet in the Enumclaw area.

The soil of Seattle, is approximately 80% glacial drift, most of which is Vashon glacial deposits, and nearly all of the city's major hills are characterized as "drumlins" (Beacon Hill, First Hill, Capitol Hill, Queen Anne Hill) or drift uplands (Magnolia, West Seattle). Boulders greater than 3 meters in diameter are rare in the Vashon till.

There are Glacial Erratics all over the area including one on Des Moines Beach that is 8 feet by 6 feet by 4.5 feet and one at Highline College that is 21 x 12 feet and is 9 feet high."

You can learn more about them on the Wikipedia page about them here.

But what about that rock in West Seattle?

Ty Swenson of South Seattle College has the answer:

"A neighbor of the college was building a new driveway when, in the process of leveling the ground, they found the very top of that massive rock.  This was back in the late 60s/early 70s when the college campus was being built out.  The neighbor asked the college if they would like it placed at the corner and they agreed. It was excavated and moved to that location."