Horn Mountains Research Articles

Relative Preference and Productivity of Species on Summer Cattle Ranges, Big Horn Mountains, Wyoming

Relative Preference and Productivity of Species on Summer Cattle Ranges, Big Horn Mountains, Wyoming

Juniper-Pinyon East of the Continental Divide, as Analyzed by the Line-Strip Method

A phytosociological study of the pinyon-j uniper association in the eastern foothills of the Rocky Mountains was initiated in September, 1951 and ended in August, 1953. Two field trips totalling over 16,000 miles in four states were undertaken for the collection of data by the firstnamed author, one during the summer of 1952 and the other during the spring of 1953. Twenty-four representative stations were analyzed for comparing the community characteristics of pinyonj uniper stands throughout the eastern range of this type except in the extreme northern portion. One of the primary objectives was the development of a sampling method sufficiently rapid for a broad reconnaissance study of a large region without sacrificing accuracy. This called for the statistical determination of adequacy of sampling. Another point considered important was obtaining reliable data on cover especially, because of its relation to erosion. These needs were met by combining into one sampling unit the line-interception principle plus a very long narrow quadrat. This unit is termed the line-strip. The main area studied extends from the Davis Mountains in Texas to the Colorado-Wyoming boundary and is bounded on the west by the continental divide. The latter forms a rather natural boundary for delimiting the scope of the problem to an area of manageable size. The area is mapped in Fig. 1, which also compares the boundary of this type as recognized by Shantz and Zon (1924) and the U. S. Forest Service (1949). Farther north, a single station was sampled in the Big Horn Mountains, Wyoming. Economically, the woodland is important mainly as grazing land; the timber has some importance as mine props, fuel,

Pegmatites of the Van Horn Mountains, Texas

Zoned and unzoned perthite-quartz-plagioclase-muscovite pegmatites in the form of tabular bodies, irregular bodies with tabular branches, irregular masses, elongate lenses, lit-par-lit zones, and small augen and stringers are distributed throughout the Precambrian metasedimentary rocks of the Mica Mine area, Van Horn Mountains, Texas. Zoned bodies have a core of perthite and quartz and a plagioclase-quartz-perthite-muscovite wall zone. The pegmatites contain numerous schist inclusions, and some show evidence of contamination by biotite schist and amphibolite.Intimate penetration of the host rock by pegmatite fluids was accomplished by a combination of dilation and digestion. Dilation was effected by injection pressure and (to an unknown degree) orogenic stresses. Crystallization of a solution containing a large excess of potash took place in a closed or restricted system where a delicate balance of solubility factors was maintained for long periods or in a solution of low viscosity, thus facilitating growth of large crystals about a limited number of centers. Zoning and textural relationships are accounted for under these conditions. The importance of horizon and mode of emplacement in the formation of pegmatite textures and shapes is emphasized. A review of the granitization, palingenesis or anatexis, open-system (or aqueous), and magmatic theories of pegmatite origin shows that the features of Mica Mine pegmatites are best explained by the magmatic theory.The Mica Mine area has possibilities of exploitation for feldspar and scrap mica.

Pleistocene Ventifacts East of the Big Horn Mountains, Wyoming

Ancient ventifacts are abundant on gravel-mantled erosion surfaces along the eastern base of the Big Horn Mountains. Stones of varied lithologic characteristics and from less than 1 inch to 6 feet in diameter have wind-cut surfaces displaying the pitting, fluting, grooving, and luster that is characteristic of ventifacts. Faces making angles greater than 550 with the wind are pitted, and faces at lower angles are grooved and fluted. As many as twenty separate faces have been cut on a single stone. In this area such multiple faces cannot be explained by wind-splitting or by variable winds, so they are attributed to changes in stone position caused largely by congeliturbation (frost action) and wind scour. Ventifacts rest on erosion surfaces at four levels, 25-325 feet above stream grade. On the lower surfaces wind-cut stones are abundant and fresh, but on the higher surfaces they are sparse and deeply weathered. At least four separate periods of wind-cutting are indicated by this evidence. Cutting is attributed to sand picked up from barren flats and hurled against stones lying in the same environment. Conditions most favorable for wind-cutting prevailed during times of glaciation in the mountains, when winds were strong and floods of meltwater inundated parts of the piedmont, producing broad barren flats mantled by sand and gravel. Ventifacts on the lower erosion surfaces are probably Wisconsin, and those on the highest surfaces may be pre-Wisconsin. Pleistocene wind directions have been measured at twenty-nine separate localities by careful reference to wind-cut faces on large, presumably stable, boulders. The mean Pleistocene wind direction so determined is N. 290 W. Modern winds are also consistently from the northwest, and it appears that local orographic control was supreme in the Pleistocene as now. Neither glaciers in the Big Horn Mountains nor the continental ice sheet, 250 miles north, exerted much influence on local wind directions.

Early Tertiary Fanglomerate, Big Horn Mountains, Wyoming

Great accumulations of coarse bouldery gravel along the east base of the central Big Horn Mountains are composed almost wholly of debris derived from the pre-Cambrian core of the range. The name "Moncrief gravel" is proposed for this deposit. It has previously been described as Pleistocene glacial material, late Tertiary to earliest Quaternary bench gravels, or the coarse phase of an early Tertiary basin fill. The gravel was found to be gradational into fine-grained early Tertiary beds and to be separated from the pre-Tertiary rocks of the mountains by thrust faults. For these reasons the Moncrief gravel is identified as an early Tertiary, probably Eocene, fan deposit, formed as the Big Horn Mountains were progressively uplifted and thrust eastward during the Laramide Revolution. Early Tertiary glaciation may have played a part, but this is largely speculation.

Geology of Wind River Mountains, Wyoming

The Wind River Mountains are made up of a core of pre-Cambrian granodiorites, except at the south end where schists predominate. On the northeast flank the dips of the sediments range from 10° to 15°. The dipping sediments range from Cambrian to late Cretaceous in age, only the Silurian being absent. Eocene, Oligocene, Pliocene, and Pleistocene overlap the older formations in some places. On the east side a series of anticlines parallels the main range about 25 miles from the summit. Minor faults affect the anticlines as well as the main range on the east side and the pattern of the lakes indicates much faulting in the pre-Cambrian core. The main uplift and folding of the range came at the close of the Mesozoic, but minor uplifts occurred during the Cenozoic. That the uplifts were irregular is indicated by the absence of Ordovician and Devonian strata at the south end, and the pinching-out, north of the range, of the Tensleep, Phosphoria, and Chugwater formations. The Lander sandstone at the base of the Ordovician in the southern end of the Wind River Mountains is absent at the northern end and thickens to 80 feet or more on the east side of the Big Horn Mountains. The glaciation and peneplanation of the range are worthy of more discussion than can be given in a short paper, and the development of the drainage lines east of the range should be treated at length. The known oil-bearing formations on the east flank are Madison, Tensleep, Phosphoria, Dinwoody, Sundance, Dakota, Mowry, and Frontier.

Grass and Timber Soils Distribution in the Big Horn Mountains1

Grass and Timber Soils Distribution in the Big Horn Mountains¹

Available Phosphorus of Soil Resulting from Moisture and Temperature Variations, Big Horn Mountains, Wyoming1

Available Phosphorus of Soil Resulting from Moisture and Temperature Variations, Big Horn Mountains, Wyoming¹

Amsden formation of the east slope of the Wind River Mountains of Wyoming and its fauna

Distribution of the Amsden The Amsden formation was described by Darton 1 in 1904 from its outcrops along the Amsden River on the east slope of the Big Horn Mountains in northern Wyoming. Since then he has described and mapped it along the Wind River Mountains from Circle on the north to south of Dallas on the south, in the Rattlesnake Mountains, and in the Owl Creek Mountains, and Blackwelder writes of its occurrence in southern Montana. According to Blackwelder, “it can be followed with more or less confidence clear across the State (Wyoming) from the Black Hills to Idaho.” 2 Only the Amsden of the east slope of the Wind River Mountains from Bull Lake southward is treated in this paper. Age of the Amsden Darton has called the upper Amsden Pennsylvanian, on the basis of fossils collected from near Leo and Shirley, and the lower part probably Mississippian. Blackwelder 3 has found two faunas . . .

Geology of the Big Horn Mountains

Previous articleNext article FreeNotes and LiteratureGeology of the Big Horn MountainsD. W. J.D. W. J. Search for more articles by this author PDFPDF PLUS Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by The American Naturalist Volume 41, Number 484Apr., 1907 Published for The American Society of Naturalists Article DOIhttps://doi.org/10.1086/278758 Views: 78Total views on this site PDF download Crossref reports no articles citing this article.

Glaciation of the Big Horn Mountains, Wyoming

Glaciation of the Big Horn Mountains, Wyoming

XLIII.—The Birds of Spitsbergen, as at present determined

I do not think it needful to give, in this Introduction, more than an outline of the voyage to which it refers. ‘The Ibis’ cannot fairly be asked to concern itself with personal adventures, but rather with an account of the birds. We left Tromsö on June 15th, sighted Bear Island about one o'clock on the following day, and on the 17th inst. fell in with light scattered ice in N. lat. 76° 10′. All that day we went through the ice, sighting, towards evening, Horn Mountain and the Spitsbergen cliffs.