Ecological Land Classification of Mount Revelstoke and Glacie r ...

ALPINE ECOREGIONThe Alpine Ecoregion occurs at elevations above the Engelmann Spruce-Subalpine Fir Ecoregion andhas the coldest, most rigorous climate as demonstrated by the lack of forest vegetation . Cool meantemperatures are inferred from temperatures at lower elevations and temperature range is probablynarrowest in the Alpine . Precipitation increases with altitude but somewhere in the Alpine the tren dmay reverse. As in the Engelmann Spruce-Subalpine Fir, most of the precipitation probably occursas snow .Wind is important in the Alpine . Janz and Storr (1977) report that areas above about 2300 m in theRockies are windy but winds may be light for several days in succession, particularly in summer. Thisis likely true of the Columbias as well and it appears that wind determines effective precipitation inthe Alpine. Most Alpine areas are exposed and snow is probably redistributed to lower elevations orto avalanche starting zones. On Bald Mountain in eastern GNP, wind exposure may be responsibl efor the unusually low elevation (about 2200 m) at which Alpine occurs. Thus, with wind as a con -trolling factor, the Alpine in MRNP and GNP may not receive significantly more effective precipitationthan Alpine areas in the Rocky Mountain parks . Within Alpine areas, complex vegetation pat -terns are often linked to varying topographic exposures and resultant snow depth variability .GEOLOGYW .S. TaylorREGIONAL SETTINGMount Revelstoke and Glacier National Parks lie within the Columbia Mountains which are in thesouthern portion of the Omineca Crystalline Belt, a central sector of the Cordilleran Orogen . TheCordilleran Orogen is a circum-Pacific orogenic belt that averages 800 km in width . It has beenevolving since the mid-Proterozoic, starting at that time as the Cordilleran Geosyncline . At present ,the region is tectonically quiet (Douglas et al. 1970) .STRATIGRAPHIC FRAMEWOR KMuch of the bedrock in MRNP and GNP was once sediment of the Cordilleran Geosyncline which isnow strongly altered. The metasediments have been grouped into rock-stratigraphic units (Okulitch1949, Wheeler 1963, 1965, Baird 1965,, Ross 1968, Douglas et al. 1970, Price and Mountjoy 1970 ,Gilman 1972, Poulton and Simony 1980) .The oldest strata make up the Late Precambrian Horsethief Creek Group . It contains some quartzite ,grit, metaconglomerate, and carbonate units, but most notable is the predominance of slate andschist. The Late Precambrian-Lower Cambrian Hamill Group occurs next in the sequence . It ismostly quartzite and contains minor slate, phyllite, schist, grit, and conglomerate . Grizzly Creek(GNP) contains one minor exposure of Lower Cambrian Donald Formation . The similarly agedBadshot Formation, though not extensive, outcrops in locations that are important because of thelimestone content . The Nakimu Caves are developed in the Badshot Formation in upper Couga rCreek. The Lardeau Group has the youngest metasedimentary rocks, possibly Middle Cambrian . Itcontains argillite, phyllite, metasiltstone, carbonate, and minor quartzite and conglomerate (all generallydark colored), but most notable are the carbonaceous slate and schist .Plutonic rocks also outcrop. Granitic rock, typically granodiorite, occurs in southwestern GNP(Wheeler 1963) and on west facing slopes above the Columbia River in MRNP (Ross 1968) . Quartzmonzonite is extensive in northcentral MRNP (Ross 1968) . The plutons probably evolved in pulsesover a long time period (Douglas et al. 1970), although a Cretaceous age has been given, probably fo rcompletion (Okulitch and Woodsworth 1977) . A body of granitic gneiss crops out in two parallelnorthwest trending bands that run from southeastern to northern MRNP (Ross 1968, Gilman 1972) .Though possibly plutonic, it may be a slice of Precambrian basement rock tectonically thrust into themetasediments . It was emplaced either prior to or during the regional metamorphism (Gilman 1972) .Okulitch and Woodsworth (1977) give a Devonian age for the gneiss .9