Pushtay on the eastern portion of the Yakima Firing Center
Topography map of Pushtay (note different name on the topo map)
A relatively small but odd hill is located east of Interstate-82 northeast of Selah, Washington on the U.S. Army's Yakima Firing Center. It is a bit hard to capture its out of place appearance. It is nearly a perfectly conical hill located on the south side of a broad slope of a large anticlinal ridge of the Yakima fold belt. The overall landscape of the area is broad sweeping valleys and ridges defined by the folded layers of basalt along with deep sharp edged canyons incised down through the folds. Hence this hill with its conical shape stands out as an oddity.
The base of the hill as well as the surrounding broad slope it rises from is underlain by the Pomona Member of the Saddle Mountains Basalt of the Columbia River Basalt Group. The Pomona basalt is approximately 12 million years old. Most of the hill itself consists of alluvial sediments that were deposited between eruptions of basalt during the upper Miocene. The particular unit on the hill is less than 12 million years old. Younger basalt lavas are present in eastern Washington; however, after the Pomona flows the volumes of later flows were substantially less voluminous. The only younger flows in the area that could have capped Pushtay is the Elephant Mountain basalt, but that flow is fairly thin in the area and may not have ever capped the alluvial sediments underlying Pushtay. The very peak area of the hill has been mapped as being underlain by Pliocene gravels that have been dated at 3.6 million years old.
The alluvial sediments that make up Pushtay were deposited by the ancestral Yakima River and perhaps also the Columbia River. The Yakima and the Columbia were pushed to the west by the repeated floods of basalt lava that filled the basin in eastern Washington. The river(s) likely was carrying a large sediment load from uplift and volcanic activity in the Cascade Range.
The Yakima River is an antecedent river. That is the river was there before the ridges formed. As south to north compression continued the Yakima fold belt lifted up the ridges that the river now cuts through. The meandering nature of the ancestal river is preserved where the river is entrenched into deeply incised valleys through the ridge areas particularly to the north of Selah in the Yakima Canyon - a classic example of entrenched meanders of an antecedent river.
Yakima Canyon topography with entrenched meander loop within Yakima Fold Belt ridges between Ellensburg and Selah
The antecedent nature of the Yakima River can be also readily be observed just north of Yakima and south of Yakima where both the river and Interstate-82 squeeze through Selah Gap north of Yakima and Union Gap south of Yakima.
Yakima River north and south of Yakima (Google maps)
A tributary stream to the Yakima (Selah Creek) is likewise entrenched in the uplifted fold very near Pushtay and can be seen on the topographic map showing Pushtay. This tributary canyon is crossed by the Interstate via a spectacular bridge.
The Yakima flows into the Columbia River. Not yet well understood changes in the area the Columbia River cuts through the Cascade Range likely caused an increase in gradient on the Yakima and thus increased the rate of down cutting by the Yakima further enhancing the entrenched nature of the current river. Possible changes on the Columbia River route through the Cascade Range may have been the result of volcanic activity.
Pushtay is a relatively isolated remnant of the old valley sediments from prior to the entrenchment of the Yakima. It is likely that the original remnant alluvial deposit that forms Pushtay was a somewhat different shape, but over the tens of thousands of years of frost action, wind and occasional sheet wash erosion from rare intense storms the hill was shaped into its current conical shape. Another factor to consider regarding the relative uniqueness of this hill is that similar features that may have once been present along the Yakima at lower elevations would have been obliterated by flood waters from the Missoula Floods that would have inundated areas below 1,200 feet. Pushtay at 1,845 feet as well the surrounding slopes would have been above the reach of the flood waters.
A look at the topographic map shows that Pushtay went by another name for many years. The name was changed to Pushtay after the Yakima Nation, Wanapum Tribe, and the U.S. Army made a request to the Board of Geographic Names for the name change in 1999. Pushtay means small mound in the local Yakima language. I have to admit the second part of the old name is descriptive and it may have been the first part that was more offensive.