The Oregon Coast has some fascinating geologic formations. The most
popular one is Haystack Rock near Cannon Beach. The ocean has been
eating away at the shoreline for thousands of years yet it left
these towering rocks stand.
What makes them different and where did the rock that created
them come from?
Approximately 17 million years ago this region was all
underwater and the shoreline was about 25 miles east of it’s
current location. The basalt that we see now in places such as
Haystack rock and the Columbia Gorge was lying underground in
molten form 350 miles away from Cannon Beach. Starting about 17
million years ago and lasting for about 10 million years a series
of eruptions from several groups of great fissures near the Idaho
border produced great quantities of lava. These flows are believed
to be some of the largest lava flows in the history of our planet.
The large amounts of basalt in these eruptions flowed across
northern Oregon along the ancient Columbia River and plunged into
the soft marine sediments. The molten basalt then spread out in
layers many miles underground and re-erupted through the seafloor
as secondary submarine volcanoes. Where the volcanic conduits were
the molten rock solidified into cylindrical intrusions creating
sheet-like dikes and sills or irregularly shaped bulbous masses.
Over the last 10 millions years the seafloor has been uplifted by
several thousand feet creating the coastal mountains and moving the
shoreline west. As the ocean pounded at the shoreline the softer
sediments were washed away leaving only the cooled molten basalt
standing. Leaving evidence of how far the molten basalt flowed
millions of years ago.
From this spot you can see a number of the towering rocks that
were created through this process. But look quick! The largest in
view rising 235 feet above the ocean, Haystack Rock, will not be
there forever. It will be reduced to rubble by storm waves sometime
in the next few millennia. Even the basalt can not stand up to the
incredible power of the ocean forever.
To log this cache please
e-mail me the name of the rock listed as #3 on one of the signs
near the coordinates or post a photo of yourself at this location.
In your log also record the number of people in your group.