Omak Lake Basin - Washington’s Deepest Natural Pit?The highest point in each state has been known for well over a century. But what about the lowest point in each state? I suppose this has been known for quite some time too (for instance, the lowest point of most coastal states—California not included—is sea level). But what if we’re not concerned so much with the lowest point with respect to the sea level datum? What if we’re concerned with determining the deepest natural pit or basin in each state? By natural pit or basin, I mean a hole in the ground—such as a crater—that has no outlet (at least on the surface) for water flow such as the rain that falls into it.
There has been much recent interest in finding out what the deepest such pits or basins are in each state (see here). I admit I was not one of the originators of the pursuit. But I now have visited three top (i.e., deepest) natural pits in Washington State.
It was in the summer of 2007 that I first heard the noise of outdoor enthusiasts clammering around in their cabin cupboards poring over their dusty maps looking for these pits. Friend John Roper was claiming at the time that he knew where the deepest pit in Washington State was. He wasn’t initially forthright with revealing his site, but with a little good natured prodding, he spilled his beans like a waterfall cascading over basalt: Bretz Waterfall Plunge Hole or what I prefer to call simply Bretz Hole. There was a stampede to visit this pit and my fiancée and I were a week behind. This hole measures out at 175-185 feet deep.
A few weeks later I had just downloaded Topo! on my car laptop and was testing it out by scrolling through the seamless maps of the Southwest Washington terrain. And there it was, staring back at me through the monitor: Bare Bottom next to Bare Mountain. Bare Mountain is about 20 miles south of Mount St. Helens. I counted the inward-spiked closed contours denoting a pit. There were fully six 40-ft contours, meaning the pit is at least 200 feet deep with a maximum possible depth of 200 + 39 + 39 = 278 ft. A field measurement in October 2007 placed the depth at around 260 feet +/- 10 ft.
Maybe three weeks later David Olson—perhaps Washington’s biggest aficionado for these natural sumps—probably whilst laboring over maps in a too-brightly lit basement, noted that Omak Lake in North-Central Washington resides in a basin. Now this area of Washington is pockmarked with little basins—usually lake-filled—whose topo map signature is the telltale inward-spiked closed contours. But Omak Lake’s basin, despite it being a “pit” without an outlet, lacks these spiked contours. This is understandable, given the basin’s size (Omak Lake covers many square miles). But nonetheless, there it is, Omak Lake and the basin it resides in may well be the deepest natural pit in the state.
So how deep is Omak Lake Basin? The depth of a natural pit is determined by two elevations: the lowest point in the pit and the lowest of all saddles rimming the pit. The lowest point of the pit is taken as the water level of a body of water in the pit if this body of water does indeed over-fill the lowest point of the pit under the water. The depth of the water itself is not taken into consideration. The lowest of all saddles rimming the pit can be thought of us as the first saddle at which water would begin to flow out of the pit if you were to fill it up, like a bathtub.
Omak Lake’s Lowest SaddleOmak Lake’s lowest saddle is located here. There is a spot elevation of 1205 feet but this does not mean the lowest point in that saddle is exactly 1205 feet or that the spot elevation was even meant to mark this lowest point. There are rock outcrops just west of the apparent lowest point. Maybe one of these rock outcrops is supposed to be where the 1205 spot was taken.
On April 19, 2008, fiancée Michelle and I traveled to Omak Lake to do a field measurement.
For the lowest saddle, we traveled south on N End Omak Lake Road. At 1.9 miles south of Hwy 155, just after passing a fancy, new high school, the road crosses a creek. Immediately after the creek there is a track on the right that drops into the field and goes across to the far end where it ends at some old farm equipment near some slabby rock outcrops. You can drive down the bumpy track without problems.
Now finding the lowest point in the saddle proved difficult given the flatness of the dale. I first ambled south a few hundred yards and made a measurement with my GPS at 1190 feet (within 36 feet of accuracy). But back at where we parked next to where the aforementioned crossed-creek makes a sharp bend from west to north, my GPS measured 1195 feet. Between these two points there runs a low ditch along the rock outcrops. While it seemed like the ditch was tilted downhill to the north, I suspect it is tilted downhill the other way. And so therefore the 1195 location is probably closer to the true saddle lowpoint. 1195 is also close to the elevation of spot 1205.
Omak Lake's ShorelineMichelle and I next traveled to the end of N End Omak Lake Road. The road ends at the north end of the lake. My mapbook shows a campground there called “Omak Lake-Mission End.” Well there isn’t really a campground there but there are some campsites on a bench. There is a wide turn around and the remnants of a boat ramp and stairs leading down from an old foundation. Evidently, there used to be more going on here than there is now. There is a wooden dock off to the left (east). You have to cross a little feeder creek to get to the dock.
Anyway, I placed my GPS on the old boat ramp slab at the shoreline and it settled out to read 941 feet. I’m going to say the lake elevation was 940 feet because the GPS was almost a foot above the water line.
Of special note was evidence that the lake level fluctuates, or at least has been higher in the past. The steeper shoreline rocks are all white for a height of about 10 feet above the lake surface. This whiteness is due to the lack of darkening lichen. Above 10 feet, the lichen takes over. I did not take the time to measure the exact height of the white line.
The USGS map gives the lake’s height as 955 feet. My GPS read 940 feet. The difference is close to the height of the white rock line.
The Basin's DepthSo what is the basin’s depth? There are a few ways to make the calculation.
If you were to just go by the saddle spot mark and the lake’s height, the basin’s depth would be 1205 feet – 955 feet = 250 feet.
If you were to use the highest contour just below the saddle and the lake’s height, the basin’s depth would be 1200 feet – 955 feet = 245 feet.
If you were to use the saddle spot and the first exposed contour lining the lake, the basin’s height would be 1205 feet – 960 feet = 245 feet.
If you were to use the highest contour just below the saddle and the first exposed contour lining the lake, the basin’s depth would be 1200 feet – 960 feet = 240 feet.
If you were to use my field measurements, the basin’s depth would be 1195 feet – 940 feet = 255 feet.
So which is correct? Well all of these and none of these. Each has an inherent error in it and without specialized (more robust) survey equipment, the exact answer may not ever be known.
If the lake were to fill up back to the top of the white rock line, the basin’s depth would be reduced by whatever amount it filled up. Conversely, if the lake level were to drop further, the amount of this drop would add to the basin’s depth.
So, is Omak Lake Basin a deeper natural pit than Bare Bottom? Based on all of the above, I would have to say yes and no. It’s a toss-up. I can say this because I’ve measured them both in the field. I invite others to make their own field measurements. Perhaps we can reach a consensus here.
--Paul Klenke, April 20, 2008