Long associated with West Seattle and it's own history, Vicki Schmitz Block shared something with Westside Seattle that predates even her family's history here.

It's a Glacial Erratic excavated from under the Third Runway at SeaTac.  She said, "It was installed in front of my house by the sidewalk for 20 years.  
I had the Port of Seattle remove it and keep it until it can be installed in the Jack Block Park."

Workers from Gary Merlino Construction unearthed the rock which geologists said is at least 250 million years old. It was put up for auction and Vicki bought it for $600. It was later delivered to her home on Fauntleroy near the ferry docks. She has since moved and the rock is now destined to be installed at Jack Block Park in West Seattle.

There is no current timeline on the move or plan as to exact location but that's the intention and wish of Vicki who was married to the park's namesake Jack Block for nearly 18 years.

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.