Glacial Erratic -- Spokane WA - Glacial Lake Missoula Flood Features on Waymarking.com

The former Northern Pacific Passenger Depot at 221 W Riverside Dr in downtown Spokane is now the Greyhound Bus Station serving distant cities.

The city has landscaped a nice plaza around the bus station. The centerpiece of the plaza is a sculpture made by Professor John T. Young of this gigantic granite erratic and a line of basalt columns, exposed when Glacial Lake Missoula's ice dam broke and the lake's waters and icebergs poured out, flooding parts of 4 US states.

This erratic probably came from the area around the city-owned Spokane Airport, where several such erratics were deposited. You can see the hole where a core sample was taken of the rock to determine if it was a mountaintop or a glacial erratic deposited by floods.

This article explains why that knowledge is important: (visit link)

"Granite Boulder in the Scablands: Mountain Top or Glacial Erratic?
By Justin Luppens

Due to the ice age floods, when a large granitic rock is found near the Spokane Airport it can be hard to determine if it is an old mountain top surrounded by younger geological features or rafted in on glaciers during the ice age floods. This may seem like an academic question, but understanding the way groundwater works in the arid West Plains or Spokane County is important to all. The deposits storing water in this region are generally composed of two types of materials: 1) the 12,000 to 16,000 year old gravel and sand deposits from the floods and 2) the approximately 15 million year old Columbia River Basalts. Hamilton and others (2004), mapped some small (approximately 60’ diameter) granitic features on the surface near Hayford road southwest of the Spokane International Airport as basement exposures. This puts constrictions on groundwater flow as granite is not readily transmissible for water.

In order to better understand the local geology and its effects on ground water, the Spokane County Water Resources decided to drill a series of small cores near several of the granite exposures in the region. This allows us to get a glimpse of the subsurface and determined whether these granitic rocks protrude upward from the basement or are from some other form of emplacement. The borings encountered basalt just beneath the granite boulders (GSI, 2014). This indicates that these large granite boulders were deposited much more recently, and most importantly, they probably do not impact groundwater hydrology of the area.

This goes to show you the picture science paints is always adapting to new knowledge. Issues like this one can have a significant impact on groundwater and painting the picture as clear as possible helps government agencies to properly allocate resources. Projects like this are a wonderful example of the Spokane County government trying to understand the resources around them and aiding in the discovery of science."

More evidence that many erratics were deposited in the Spokane area can be found here: (visit link)

The sculpture is featured in the Bringing Home the Wishing Rock earthcache: (visit link)

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Date Logged Log User Rating   02/22/2022 Benchmark Blasterz visited it