Lake History - Features	Elevation	Age or Era
USGS Map N4115-W11915 7.5-minute series Today, the lake is much lower and smaller than this.	4,894ft. 1491m	26ybp
Approximate Modern Outlet This streambed is almost flat and slopes little until the Potholes.	~4,884ft. 1488m	today
Approximate level of highest shoreline after landslide.	~5,140ft. 1566m	~11,200ybp
Pleistocene High Rock Lake Well developed shoreline features, eroded. Numerous beaches, soils.	~ 4,890ft. 1490m	§ 1.5-million? to 11,200ybp
Pleistocene Upper High Rock Basin Lake Deposits Diatomaceous? deposits visible on hillsides.	~ 5,850ft. 1782m	§ 3-million? to 1-million ybp
Pleistocene Cottonwood Creek Basin Lake Deposits Crustal algae deposits on old beach rocks. More extensive diatomaceous earth deposits on lee shores	~ 5,600ft. 1706m	§ 3-million? to 1-million ybp
Wono Bed/Member Tephra - a key layer for the current research; quite thick and easy to identify.	~10 cm thick ~1-4m below today's surface	C14 dates above and below circa 33,650+-720ybp to 24,480+-430ybp.
This small lake, in many respects a remnant of a previous era, is another minor but important episode in millions of years of geologic changes here. There was a landslide of pretty massive proportions which allowed a lake to form and to rise and cut a new outlet miles away from the original. Mifflin and Wheat (1976) reported this as a Lahontan time event. Researching the geologic area map from Ach et.al.(1991) was the postulation that the landslide was an early Pleistocene or Late Tertiary event, whoa, quite a difference. This later map also stated a general concept of graben valley and fault blocks rising.     There may not have been a continuous lake, yet any change of outlet sets the stage for examining the valley's stratigraphy for evidence of the geologic and human past from the landslide event as a marker. For a report on this trip, click <<Geologic History>>     The valley's unique history can provide an opportunity to find out a lot about the past. This area was rife with game and other food sources the farther into the past you study due to climate in general, but also by the lower level of the southern Cascades to the west (it was wetter, supporting Sequoias where today you find at best piñon and juniper). It also had rather permanent lakes, so offers good hunks of the past in ancient lake sediments. If no Pleistocene lake existed, then the sediments from the landslide lake should be the depth below the present valley floor to the floor of Box Canyon, several hundred feet or more, plus the difference of the graben drop. That's a lot of history. The grade from Little High Rock Canyon at the high water mark to the present floor of Box Canyon is about 400'/31000', 0.0129:1. From the upper entrance of Little High Rock to this high water mark is about 120'/15000', 0.008:1. This is about a third the grade across to Box Canyon. This change of river grade of course would erode faster than the lesser grade. From the head of Box Canyon out the grade is 400'/17000', 0.0235:1, almost double that, meaning the greatest erosion should have occured in this rising block section.
The previous outlet, today's Box Canyon, provides a very stable and old erosional surface, one with a very steep cliff for a headwall. If this headwall was from the landslide closing the canyon, it should be easily seen in the rocks. But the area suggests a previous lake level; some rather large beach steps on the northern side of the valley where wave erosion was highest exist, and remnant strand lines at the same elevation around the valley are also evident. Also, geologic maps of this valley have it as Quarternary deposits, mainly lacustrine (lake sediments) and alluvium.     Diatoms and algae within the cores will establish if this was the case, or if no previous lake existed and the outlet was just a stream and the only lake existed only after the landslide. In any case, from seeing the place, it today gives the impression that the outlet stream was over a lip of hard rock and contained a lake behind it at about 5,000ft elevation. The low point of the landslide is about 130ft higher with a sink hole down to 5,018ft near it's middle, one of the clues that it's a landslide. Quite interesting.     After the landslide, the lake rose enough to find a way over the softer and not-so-uplifting rocks to the north to drain the lake steadily through downcutting, never again flowing out Box Canyon. The downcutting was fueled by perhaps triple the volume of the 5,000ft lake level volume. I have found wave erosion remnants miles up High Rock Canyon (these also are on the Ach map). So, this was a major change to some of the living places available, if anyone was around before the landslide, their artifacts likely would have changed locations in more recent times from before. If there was a previous lake, the evidence will be near the old lake level, if no lake existed before, or changed level radically, then the evidence would change locations accordingly from outlet streamsnote. In any case, the sediments hold the answers here, this wasn't a pluvial lake system in that it existed in spite of pluvial conditions, yet it surely has dried out during the past eleven thousand years.     But, this is very recent geologic history for this area, which has old basalts overlain by volcanic ash and rhyolites, and old erosional surfaces in cake layers. It also appears to have had two large, and perhaps shallow lakes filling the upper basins which fed Little High Rock, Smoky and High Rock Canyons, the one in Cottonwood Creek basin having large diatomaceous earth deposits and beautiful beach steps for miles as a result. Uplift and plateau tilt also has been ongoing at times and would have altered erosional conditions. Still, these canyons are rather classic examples of uplifting mountains being cut by streams as they rise, especially Box Canyon where the valley walls average 500ft high cliffs with a flat valley floor that averages 200ft wide. Notably, the outlet canyon is mirrored by Little High Rock Canyon, suggesting a fault through both pieces of the tilting blocks.
With the block fault sections tilting towards High Rock Lake or easterly, the streams in the two basins eventually wore through the intervening basalt to form the modern canyons. In this later stage, I assumed there was a High Rock Lake which filled most of Smoky Canyon and was relatively stable as the outlet was rising (or graben falling), thus keeping up with erosion compared to today's valley. Today the valley essentially holds a very small remnant lake whose outlet is about 30m lower than my guess at a stable level, while the landslide level was another 140 feet higher than that. Either way it also left diatomaceous earth deposits at its northern end which are likely dating to the landslide, much younger than those in the Cottonwood Creek basin by a million years.
Now to mention again the headwall in Box Canyon. It's importance is that whatever level the bedrock at its top, that was the outlet height for the lake contained behind it if the canyon wasn't closed by the landslide. The estimate is bedrock to 100ft.higher than today's lake, which is what was lost as the water created Fly Creek. Yet, I have to downclimb the headwall to find out if it's landslide all the way. There certainly have been changes in climatic conditions, but with plenty of water, the lake today would still be 100ft. below this strandline level. This, if true, creates a pretty large lake, some 10 miles long in Smoky Canyon, about 2 miles up Little High Rock and 10 or more miles up High Rock Canyon when full (it worth assuming it dried out at times).
For a view of the archeology from a recent trip, <<Click Here>>

Questions or comments are welcome, email them to Tom Mallard
© Mallard, 1998, Seattle, USA

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