While riding through Central Washington (south of Moses Lake), I noticed some rock towers that looked a little like Devils Tower in Wyoming. I was very curious about what caused them- I remember very little from my college Geology 101 class.

The basalt formations are shown on this page, as well as some images of Pothole Lakes and the surrounding hex-shaped basalt cliffs.

James Perkins of the Portland area answered my plea for help. James describes himself as a "hobby geologist". The following text is his, unless prefaced with [square brackets].

I've had a hobby geologist's interest in the area since I was a kid. The scablands of Eastern Washington are the results of Fire, Faults, and Floods, in more or less that order. There's a book of the same name -- this provides an excellent introduction to the geology of the area. You may also want to pick up Roadside Geology of Washington and Roadside Geology of Oregon, and the book Northwest Exposures by Alt and Hyndman. One more book, Cataclysms on the Columbia, is a good read too.

The basalt got there from the Grande Ronde and other volcanics that flooded the entire region of Eastern Oregon and Washington from about 17 to about 6 million years ago. These volcanics flowed as far as 300 miles to the ocean (notice Oregon City, the hills South of Salem and also most of Portland's West Hills are composed of the flood basalts) where prominent headlands of the North and Central Oregon coast are formed from them (so is Saddle Mountain in NW Oregon). The lava tunnels even burrowed down between sediments then were erupted upward again at the haystacks, leaving pillow basalts when erupting undersea. There are also plugs from the dikes which form the haystacks.

During this time the Cascades were mostly gone... they erupted from 25-30 million years ago, then subsided and flattened out, then only recently did the Cascades become active (5 million years ago to present) and this bulged up the whole mountain range again. So you can see that there was a sizable gap from 17 to 6 million years ago when the flood basalts could flow West with being less impeded than they would be today.

Also during the last 10 million years or so there have been crustal compression in Eastern Washington and Oregon, which have raised long folds -- the John Day Valley flows through one low point, the Horse Heaven Hills and Yakima hills are all these structures. It's effectively pushed up the flood basalts 1000' at the ridge tops. Some rivers like the Yakima refused to be perturbed, you can see North of Yakima where the River just cut down through the raised hills. The same thing at Picture Gorge where the John Day River cuts right North through the mountains that folded up in its path.

The Columbia River and Palouse pretty much tried to keep paths heading West until they ran into the Cascades, then South to the Oregon Border, then West. The Columbia used to flow through the Salem area and come out around Lincoln City, for atime, and flood basalts kept flooding it and moving it until it went back to the channel it has today. The Columbia also kept being pushed up the Cascades in Washington and then eroding back down through the basalts. There are a couple major channels in Washington that the Columbia flowed through, seperated by tens of miles.

So why does the Palouse head South today instead of West to the Columbia like it used to? And why does it have an amazing gorge? And why the high basalt buttes with basalt rubble around and below them? And why the dry falls and the wide, wide U-shaped valley of the Columbia all the way to the ocean? And why the channeled Scablands?

J. Harlan Bretz answered the questions above when he observed it looked like a monumental flood had went through the region. And not just once but 50-60 times. Each time it rerouted the Columbia a bit, chopped through the Palouse soils to the basalt bed, and even tore up the basalt bed. It left channels 500 feet above the current Columbia River on the hills above. It temporarily formed a lake in South Central Washington, and the Willamette Valley, especially the Portland, Lake Oswego and Tualatin areas, were filled with gravel and sediment that backed up to Eugene and left glacial rocks from Montana perched on hilltops where glaciers grounded. The source was all in the Western Valleys of Montana, which filled up with a mile deep lake when a glacier cut off the valley. When the glacier collapsed the lake, with dozens of cubic miles of water, emptied -- in the course of a couple weeks -- leaving gravel bars a hundred feet high as it flowed at 30-40 mph. The Palouse channel that went West wasn't broad enough to take the flow so the major flood headed South, cutting through a 5-mile wide sheet of basalt and digging down through several flows to make the present Palouse valley.

For more on this story, read some of the books above. They are all fascinating.

[I asked: So the basaltic outcroppings are simply "islands" from the erosion of the big flood?]

Just looking at them out of hand I'd say yes, although I'd have to go look at the specific area and compare it to the books to say yes.

All the bare basalt in the Columbia Gorge and Lower Snake River, and especially Dry Falls, Pothole Lakes, the Palouse Valley -- all are huge flood remnants. The Dry Falls had several hundred feet of water going over the lip at its height.

[I asked: What causes the formations near Pothole Lakes? In other words, why right there, and why are the rocks in vertical columns?]

Good question. First off, basalts are runny and spread out (go to Hawaii you can see this in action in a moderate but persistent scale). They form lakes and broad flow fronts depending on how flat the terrain is they flow over. So, you have this large pool of lava. Think of it like a pool of candle wax. It starts to freeze (crystallize, we say with rocks) at the top where the air cools it, and at the bottom where heat is conducted into the earth. So, the mass cools toward the middle.

Like any other physical compound, as it cools and changes into a solid phase, it shrinks. Candle wax is still plastic enough when it solidifies that it forms a nice slab, a bit thinner than it was when it was liquid. Rock also forms a slab that's slightly thinner, but it crystallizes into rigid structure. It is more brittle and has a higher tensile strength than candle wax, so as it shrinks, it fractures. First, it fractures at the outside edges (top and bottom of the lava flow exposed to the coolest temperatures). These cracks naturally break the top and bottom into polygonal shapes - hexagons being pretty common, but any number of sides is possible. As it continues to cool toward the middle the cracks continue until you get to the last few feet or inches, which because it is an interface between the lower crack system and the upper system that don't line up -- looks all jumbled.

So, one lava flow turns into three main slabs... the top part of columns is called the tablature. The bottom part is called the colonnade. [We'll call] the middle part [...] the interface. So, the columns are standard basalt habit.

If you've ever taken Highway 3 by the way from Lewiston/Clarkston to Enterprise you'll actually travel down into the heart of the huge basalt volcano and back out, plus it's an awesome drive. Also, the Imnaha Valley and up to the Snake River Canyon overlook is part of the same massive flood basalt system. In it you'll see dozens of layers of basalt flows, often with a thin layer of soil between them. The Columbia Gorge also shows them off well. There are other large flood basalt areas in the Deccan Traps of India, and in Siberia, we are lucky to live on and in one.

Other quickly-deposited slabs of fairly uniform volcanic rock will do this columnar fracturing if it is quickly deposited on a surface slab... like rhyolite lava flows (glassy) that you can find in the John Day area (Fossil, Oregon) or the Yellowstone River Canyon - that's what comes to mind right away. Usually rhyolite is lighter in color -- it's much more glassy and "clinks" while basalt is heavier, usually darker. Also, being in the way of most rhyolite eruptions is way more terrifying than being next to a basalt vent.... but I digress.

Now think of many layers of basalt with soil between them: starting from the bottom, a sort of giant layer cake (or a lasagne, mmmm, lasagne): a flow that has colonnade and interface and tablature, a thin layer of soil where trees and plants got a hold, then another lava flow with colonnade, interface, and tablature, then another thin layer of soil, and so on. Repeat a dozen or two dozen times. When you ride down the Columbia canyon it's all around you. It's hiding under Portland and exposed some in the West Hills due to uplifting. It's hiding under the Palouse hills.

Anyway, now take several hundred feet of water, icebergs, glacial boulders, and zoom them across the soft soil of the Palouse. Imagine a wall of water 200, 300, 400 feet high, and it stays that high behind it for a week or two. In hours the Palouse soil becomes mud (mixed with anything living that was there) in a heavy slurry at the bottom. Now you're down to the tablature of the basalt underneath.

Basalt columns always have some relief, and when you put mud, trees, boulders the size of houses, and icebergs and several hundred feet of water moving at 30-40 miles per hour over the top of that basalt, it will start to tear columns out. It will even break the columns loose at their base and suck them out. The columns will spin under the force of the water and loosen their neighbors. If the flow has any swirling to it, these massive columns will swirl around and around in the widening hole, knocking a whole wide ring of columns out. Many of the plucked massive columns continue on in the flood (which is at this point a humongous debris flow). There's plenty of rubble to go around. Other columns continue their work, remove the thin layer of soil, and begin plucking and ripping out the rock slab below them.

In the Palouse Canyon near the falls you see as you get closer to the River channel, it cuts out successive rows of columns in a giant stair step down to the River. The weakest points are the soil layers beween the lava flows, that's why it ends up in a stair step shape.

In Pothole lakes, they are actually potholes. Just like in a mountain stream that crosses rocks, where pebbles find a recess and spin around and around widening the hole into a broad cup. The Pothole lakes are the same thing magnified by many orders of magnitude and scoured by basalt slabs as big as a semitrailer spinning around in the flow.

[Again, a big thanks to James Perkins for providing this information. I keep learning more every time I read it.]