Spear (Lane Mountain complex)
Publicado 2023-07-07
Spear.
East of the main mass of the Lane Mountain complex is a very smooth eroded plain of granitic basement rock that starts from Superior Valley and very gradually rises for several miles southward towards and up to the Mud Hills. This elevated and gradually sloping plain has been referred to as the Williams Plain.
Spear and Mesa (Mesa Benchmark), the most prominent features in the Williams Plain, are two large buttes along the pain's western boundary. Both buttes are capped with andesitic porphyry (Lane Mountain Andesite), which has been highly resistant to erosion. The andesitic lava acts like a protective cap over the original surface immediately beneath it and is comprised of the quartz monzonite basement rock. The Lane Mountain andesite is estimated to have been erupted possibly sometime during the late Pliocene. Recent studies have more accurately dated other flows in the vicinity of the Lane Mountain complex (to include the latite making up Lane Mountain) to be of early Miocene, so it is possible that the flows represented at Spear and Mesa Benchmark were emplaced prior to the late Pliocene.
At least two theories have been proposed how both buttes came to be:
The first theory suggests that the andesite capping both buttes are vestiges of a larger flow that may have occupied much of the Williams Plain.
The second theory suggests that the andesite was extruded (erupted) from a localized vent and may have occupied areas not much larger than they are now. The vent(s)/plug(s) are then likely beneath the exposed andesitic rock. This theory is believed by some geologists to be the most plausible due to the absence of fissure dikes and the lack of andesitic porphyry of the same type found within the Williams Plain and surrounding area.
It is possible that the Lane Mountain Andesite shares a relationship with other andesitic porphyry that has been extruded around the same time in neighboring areas such as those found within and around the Lava Mountains, Red Mountain, and Almond Mountain. I would be willing to surmise without further reading that the conditions that produced the Lane Mountain Andesite are not unlike those of the same age found elsewhere.
Around the Lane Mountain complex area are additional lava flows of varying composition, all of which overlay the older rock similarly. This includes the porphyritic latite that makes up most of Lane Mountain. These separate flows have all been bracketed under the description of the Lane Mountain Volcanics. It is because of this relationship and categorization that I have included Spear and the Mesa Benchmark in this series.
The Williams Plain area is an Area of Critical Ecological Concern (ACEC). The objective of the designation in this area is to protect the Lane Mountain Milkvetch. This plant is endemic to the areas of the Lane Mountain complex and western areas of the Paradise Range. The plant is listed as an endangered species.
References:
Burke, D. B., J. W. Hillhouse, E. H. McKee, S. T. Miller, J. L. Morton, Cenozoic rocks in the Barstow Basin area of southern California-Stratigraphic relations, radiometric ages, and paleomagnetism, U.S. Geol. Surv. Bull., 1529-E, 1– 16, 1982.
Dibblee, T.W., Jr., 1967, Areal geology of the western Mojave Desert, California: U.S. Geological Survey Professional Paper, 522, 153 p.
Dibblee, T.W., 1968, Geology of the Fremont Peak and Opal Mountain quadrangles, California: California Division of Mines and Geology, Bulletin B-188, scale 1:62,500
Dibblee, T.W., and Minch, J.A., 2008, Geologic map of the Opal Mountain & Lane Mountain 15 minute quadrangles, San Bernardino County, California: Dibblee Geological Foundation, Dibblee Foundation Map DF-403, scale 1:62,500.
Stone, P., Brown, H.J., Cecil, M.R., Fleck, R.J., Vazquez, J.A., Fitzpatrick, J.A., and Rosario, J., 2019, Geochronologic, isotonic, and geochemical data from igneous rocks in the Lane Mountain area, San Bernardino County, California: U.S. Geological Survey Open-File Report 2019-1070, 34 p.
All photos and videos were taken by Alexander F. O'Connor.
Soundtrack by Alexander F. O'Connor.
Video produced using Movie Maker (Version 2012) by Microsoft Corporation.
Music production, mixing, and editing made possible using Music Maker (64-bit) Version 32.0.0.2 by MAGIX Software GmbH.
Full trip report:
peakbagger.com/climber/ascent.aspx?aid=2239467
This series is dedicated to the loving memory of my mother, Erin P. O'Connor.
Thank you for watching.
Todos los comentarios (4)
-
Great video! "on a scale of 1-10...... 10 alright lets go"😅
-
Like the music in this one. Vaguely reminded me of the original Bladerunner soundtrack
-
Where is that place? I WOULD FIND PLACES SIMILAR AND TELL JESUS I NEED YOU! rave BOB JONES DIVINE ENCOUNTERS and ROBERTS LIARDON he prayed for me in Nampa IDAHO.
