Tualatin Mountains Geologic History EarthCache
Hidden : 9/5/2012
Difficulty:
1 out of 5
Terrain:
1 out of 5

Size: Size: not chosen (not chosen)

Join now to view geocache location details. It's free!

Watch

How Geocaching Works
Looking for a different adventure?

Related Web Page

Please note Use of geocaching.com services is subject to the terms and conditions in our disclaimer.

Geocache Description:

This Earth Cache will take you 260 feet under ground and 15.6 million years into the past to explore the Geological History of the Tualatin Mountains!

A core sample is a cylindrical section of (usually) a naturally occurring substance. Most core samples are obtained by drilling with special drills into the substance, for example sediment or rock, with a hollow steel tube called a core drill. In the coring process, the sample is pushed more or less intact into the tube.

The Grande Ronde Basalt formation is one of the most expansive basalt formations on Earth. It was laid down about 15.6 million years ago. The Robertson Tunnel, Tri-Met MAX stop at Washington Park, has a core sample on display that describes the history of the rock formations in the Tualatin Mountains. The station is the deepest underground station in North America, at a depth of 260 feet, and is constructed amidst the Grande Ronde Basalt Formation.

To get credit for this Earth Cache, you must visit the site, read the posted plaques at the core sample, and email the answers to the following questions to the cache owner (click cache owner's name and click Send Message):

1. The tunnel lies in the Grand Ronde Basalt Formation. How many separate lava flows make up the Grande Ronde Basalt Formation? Which two flows shown in the core sample are part of the Grande Ronde Formation?

2. What is the name of the layer left during the green period that followed the Grande Ronde Basalt Formation? How long did this green period last?

3. What was the name of the basalt flow that ended the green period from question 2?

4. How long ago did retreating glaciers deposit a layer of silt in the Portland Hills? Hint: "This layer accumulated between x and possibly y years ago"

This cache is wheelchair accessible and can be reached by public transportation or parking at Washington Park (zoo).
For more information about the Geological history of the area (advanced), please refer to the USGS report available at: http://pubs.usgs.gov/sim/3144/

COGRATS TO ZERO MONTANA ON HIS 1St EC F2F!

Additional Hints (No hints available.)



Advertising with Us

Inventory

There are no Trackables in this cache.

View past Trackables

What are Trackable Items?

Bookmark Lists

View all 38 bookmark lists...