South-central British Columbia Research Articles

Structure and dynamics of a nearly steady-state subalpine forest in south-central British Columbia, Canada.

We examined the size, age, and spatial structure of trees in an old Engelmann spruce (Picea engelmannii)-subalpine fir (Abies lasiocarpa) forest based on four stem-mapped, 0.25ha plots. Dendrochronological techniques were used on basal discs of 1,190 trees to reconstruct age and growth pattern, including dates of rapid growth increases. There were no obvious age cohorts or other evidence of past major disturbance. The abundance of both subalpine fir and spruce decreased rapidly with age, especially beyond the ages of 150years. Very old trees were present, but rare. The best evidence from tree-ring width patterns for past disturbance was a period of release 100years ago. However, few of the released trees grew into the canopy, which suggests a disturbance of low intensity. Patch dynamics and gap processes were not pronounced in the stand. Clumping was generally weak and only present at small spatial scales (<5m) for live trees, and largely non-existent for dead trees; mortality was spatially random in this forest. Although spruce were sparse (5.1% of trees) in the forest relative to fir, which is consistent with predictions that fir will ultimately replace spruce in the absence of disturbance, coexistence seems more likely judging from the age structure and numbers of dead trees. In contrast to almost all spruce-fir forests studied previously, the stand we examined showed no record of major disturbances. Thus this stand falls at the limit of the range of dynamics - from disturbance-structured to near steady-state - encompassed in current thinking about forest ecosystems.

Water: A First Nations' Spiritual and Ecological Perspective.

Water quality and availability is an urgent global concern. This paper documents, through the use of ethnographic research methods, First Nations� concerns and perspectives about water. The paper�s scope is primarily limited to the views of three Elders from the southern Interior of British Columbia: Mary Thomas from the Secwepemc, Millie Michell from the Nlaka�pamux, and Mary Louie from the Syilx Nation. Secondary literature sources complement the Elders� sharing of Traditional Ecological Knowledge (TEK). The Elders� emphasis on the spiritual impor-tance of water is contrasted with Western science�s emphasis on water�s unique physical and chemical properties. This fundamental difference raises questions about Western science�s approach to freshwater ecosystem management and study. Ultimately, this paper documents the wisdom of highly respected Elders about water in relation to the culture and freshwater ecosystems of South-Central British Columbia.

Influence of conventional and chemical thinning on stand structure and diversity of plant and mammal communities in young lodgepole pine forest

Silvicultural practices that provide a wide variety of vegetative composition and structure (habitats) in young stands should help manage for biological diversity across forested landscapes. This study was designed to test the hypotheses that: (i) abundance and diversity of stand structure attributes (species diversity and structural diversity of herb, shrub and tree layers) and forest floor small mammal communities, and (ii) relative habitat use by large herbivores, will increase from unthinned to conventionally thinned to chemically thinned stands of young lodgepole pine ( Pinus contorta) forest. Replicate study areas were located near Summerland, Kelowna and Williams Lake in south-central British Columbia, Canada. Each study area had three treatments: a conventionally thinned, a chemically thinned and an unthinned stand. Pre-commercial thinning was conducted in 1993. Coniferous stand structure and understory vegetation were measured prior to thinning in 1993 and 5 years later in 1998. Small mammal populations were sampled intensively from 1993 to 1998. Relative habitat use by large herbivores was sampled in 1998. Our results indicate that chemical thinning of young lodgepole pine stands produced an aggregated pattern of crop trees compared with stands subjected to conventional thinning. Diameter growth of crop trees in the chemically thinned stands was similar to that in the conventionally thinned, but also to that in unthinned stands. Although horizontal stratification (aggregates of trees) was enhanced, vertical stratification (structural diversity of vegetation) was less in the chemically than conventionally thinned stands. Abundance and diversity of understory vegetation and small mammal communities were generally unaffected by stand thinning in these particular installations. Relative habitat use by mule deer ( Odocoileus hemionus) occurred in a gradient from highest in the conventionally thinned stand to lowest in the unthinned stand. Habitat use by snowshoe hares ( Lepus americanus) tended to have the opposite trend. Moose ( Alces alces) exhibited no difference in habitat use among stands. Thus, although there were few differences among treatment stands, chemical thinning could be used to develop an aggregated pattern of crop trees in pre-commercially thinned stands to maintain habitat for herbivores such as snowshoe hares and mule deer. Understory plant and forest floor small mammal communities would be maintained in these stands as well.

Reconsidering the Cause of Cultural Collapse in the Lillooet Area of British Columbia, Canada: A Geoarchaeological Perspective

The potential interconnections between human settlement systems, subsistence practices, and rapid, high-magnitude transformation of the physical landscape (e.g., earthquakes, volcanic eruptions, and landslides) is an important issue of discussion in archaeology. This paper critically examines the argument that prehistoric abandonment of Classic Lillooet pithouse villages of south-central British Columbia, Canada, at approximately 1200-1000 B.P., was linked to one or more catastrophic landslides at Texas Creek that blocked the Fraser River, destroyed salmon resources, and caused the abandonment of this area. Examination of the location and depositional condition of several excavated archaeological sites within the Fraser Valley, as well as reflection on the expected environmental and cultural responses to a catastrophic landslide, challenge previous interpretations of the existence, location, and magnitude of such a landslide event, and indicate that archaeologists need to reconsider deterministic environmental explanations for the abandonment of pithouse villages in the interior of British Columbia.

STAND STRUCTURE AND SMALL MAMMALS IN YOUNG LODGEPOLE PINE FOREST: 10-YEAR RESULTS AFTER THINNING

Management of forested landscapes for biological diversity is a major objective across North America. Perhaps the greatest potential to diversify future forests lies in the vast areas of young second-growth stands which may be managed silviculturally to accelerate ecosystem development. This study was designed to test the hypotheses that large-scale precommercial thinning, at ages 17–27 yr, to various stand densities would, over the 10-yr period since treatment, enhance: (1) productivity of lodgepole pine (Pinus contorta) crop trees, (2) stand structure attributes, and (3) species richness and diversity of forest floor small-mammal communities. Study areas were located near Penticton, Kamloops, and Prince George in south-central British Columbia, Canada, in three forest ecological zones. Each study area had three stands thinned to densities of ∼500 (low), ∼1000 (medium), and ∼2000 (high) stems/ha, with an unthinned juvenile pine and old-growth pine stand for comparison. Understory vegetation was measured in all stands in 1990, 1993, and 1998, and coniferous tree layers were measured in 1998. Small-mammal populations were sampled intensively in 1990, 1991, and 1998. Mean diameter increments of trees in the low-density stands were significantly higher than those in the medium- and high-density stands at all study areas. Mean height increments of trees were similar in the medium- and high-density stands and significantly higher than that in the low-density stands at Penticton and Prince George. Crown volume index (biomass) of herbs was highest in the thinned stands by 1998, but there was no difference among stands for shrubs and trees; volume of mosses was highest in the old-growth stands. Mean species richness and diversity of herbs, shrubs, and trees were similar among stands at 2, 5, and 10 yr after thinning. However, mean species diversity and structural diversity of coniferous trees were significantly higher in the low- and medium-density stands than in the high-density and unthinned stands 10 yr after thinning. Total structural diversity of all vegetation in the low-density stands was significantly greater than that of the medium-density, unthinned, and old-growth stands in 1998. Mean total abundance of all small mammals was similar among stands in 1990–1991, but the low-density and old-growth stands had the most mammals in 1998. Mean abundance of southern red-backed voles (Clethrionomys gapperi) was consistently higher (2.1–3.3 times) in the old-growth stands than in unthinned stands. In seven of nine cases, mean abundance of red-backed voles was similar among old-growth and thinned stands. Mean species richness and species diversity of small mammals were highest in the low-density and medium-density stands. Heavily thinned lodgepole pine stands developed structural attributes such as large diameter trees, large crowns, and structurally diverse vegetative understories. Forest floor small-mammal communities reflected the compositional and structural diversity of these managed stands.

Diatom, Pollen, and Chemical Evidence of Postglacial Climatic Change at Big Lake, South-Central British Columbia, Canada

Postglacial climatic conditions were inferred from cores taken from Big Lake in southern British Columbia. Low concentrations of nonarboreal pollen and pigments near the base of the core suggest that initial conditions were cool. Increases in both aquatic and terrestrial production suggest warmer and moister conditions until ∼8500 cal yr B.P. Hyposaline diatom assemblages, increases in nonarboreal pollen, and increased concentrations of pigments suggest the onset of arid conditions from ∼8500 to ∼7500 cal yr B.P. Slightly less arid conditions are inferred from ∼7500 until ∼6660 cal yr B.P. based on the diatoms, small increases and greater variability in biogenic silica and pigments, and higher percentages of arboreal pollen. At ∼6600 cal yr B.P., changes in diatoms, pigments, biogenic silica, and organic matter suggest that Big Lake became fresh, deep, and eutrophic until ∼3600 cal yr B.P., when water levels and nutrients decreased slightly. Our paleoclimatic inferences are similar to pollen-based studies until ∼6600 cal yr B.P. However, unlike these studies, our multiple lines of evidence from Big Lake imply large changes in effective moisture since 6000 cal yr B.P.

Lithostratigraphy and limiting optical ages of the Pleistocene fill in Fraser River valley near Clinton, south-central British Columbia

The Fraser River valley near Clinton contains a thick sediment fill that is presently incised down to bedrock. The sequence, approximately 500 m thick, is generally upward fining and consists of up to 100 m of glacigenic debris flow diamicton and glaciofluvial–deltaic gravel and sand at the base, overlain by about 350 m of glaciolacustrine sediments and minor diamicton, which is in turn capped by several metres of till. The sequence is interpreted to represent (i) valley aggradation in response to glaciation, followed by (ii) the impoundment of the valley by sediment and (or) ice, and the formation of a large proglacial lake(s), and finally (iii) overriding of the valley fill by glaciers. This glacial advance sequence can be readily correlated with previously studied units situated immediately to the north, most of which have been associated with the last glaciation; however, the age of these units has been based only on stratigraphic relations. We introduce limiting optical ages from a widespread glaciolacustrine unit that show that the glacial advance sequence was formed, at the earliest, during the penultimate Okanagan Centre Glaciation (oxygen isotope stage 4; ca. 74–59 ka), but almost certainly during the (last) Fraser Glaciation (oxygen isotope stage 2; ca. 24–12 ka). It could not have been deposited during oxygen isotope stage 6, or during an older glaciation.

The conglomerate of Churn Creek: Late Cretaceous basin evolution along the Insular–Intermontane superterrane boundary, southern British Columbia

Upper Cretaceous coarse clastic rocks exposed in the canyon of Churn Creek, south-central British Columbia, record active basin tectonism and coeval volcanism adjacent to the boundary between the Intermontane and Insular superterranes. Mid to late Albian (~104 Ma U–Pb), calc-alkaline andesite and basaltic andesite flows, with minor conglomerate and reworked epiclastic deposits and tuffs correlative with the Spences Bridge Group of the Intermontane superterrane are exposed in the canyon. In depositional contact above the volcanic rocks is the conglomerate of Churn Creek, which contains a thick (&gt;1 km) sequence of complexly intertonguing conglomerate and sandstone that is divided into two members composed of four lithofacies. The lower member was deposited unconformably on the underlying Albian volcanic unit and contains late Albian–Cenomanian chert-pebble (&gt;50% chert) conglomerate and interbedded chert- and volcanic-lithic sandstone. It is interpreted to have been deposited in a braided stream system flowing from southeast to northwest. The source for the chert was most likely the Bridge River terrane, a Mississippian to Jurassic ocean floor assemblage located to the southwest of Churn Creek, south of the Yalakom fault. Gradationally overlying the lower member throughout much of the basin is a mixed chert, plutonic, and volcaniclastic lithofacies of the upper member. Plutonic debris was provided to the mixed and plutonic lithofacies of the upper member by the Little Basin pluton, which was uplifted along the northeast-directed Little Basin thrust fault on the southwest margin of the basin. The upper member also contains a volcanic-rich lithofacies composed of chaotic volcanic conglomerate and local lithic tuff derived from a coeval proximal volcanic source. The conglomerate of Churn Creek records active northeast-vergent compressional tectonism and development of piggyback basins along the boundary between the Insular and Intermontane superterranes during Albian–Santonian time. The conglomerate of Churn Creek has been correlated to the Silverquick – Powell Creek succession of the Methow terrane, based on age, stratigraphic, lithologic, structural, geochemical, and paleomagnetic similarities, and may, therefore, represent an overlap assemblage linking the superterranes in the Late Cretaceous.

Geological and geochemical evidence for variable magmatism and tectonics in the southern Canadian Cordillera: Paleozoic to Jurassic suites, Greenwood, southern British Columbia

The Paleozoic and early Mesozoic rocks of the Greenwood mining camp in southern British Columbia are a part of the Quesnel terrane in the eastern part of the Intermontane Belt of the Canadian Cordillera. Upper Paleozoic rocks include the Knob Hill Group composed of oceanic tholeiitic basalts (with (La/Yb)n [Formula: see text] 0.4–1.2), associated with deep ocean sedimentary rocks and serpentinites; the Attwood Group that comprises island-arc tholeiites (with (La/Yb)n [Formula: see text] 1–4 and positive εNd values), clastic sedimentary rocks and limestones; and a unit of oceanic gabbros with (La/Yb)n &lt; 0.5. These lithologically defined units occur as tectonically emplaced slivers of oceanic crust probably produced during the closure of the Slide Mountain basin during the Permian. They are unconformably overlain by Middle Triassic calc-alkaline volcanic and sedimentary rocks of the Brooklyn Group. The Brooklyn Group volcanic rocks have characteristics of mature island-arc rocks, including (La/Yb)n [Formula: see text] 2.5–4.5 and positive εNd values. The Paleozoic rocks are crosscut by a 200 million years old granodioritic intrusion containing zircon with an Early Proterozoic inheritance age (~2.4 Ga). By inference, southern Quesnellia may have been well offshore from the ancestral North American margin in the Mississippian, in close proximity to the margin by the Middle Triassic, and contiguous with it by the Early Jurassic. It is suggested that the complex tectonic history of extension and contraction of the southern Canadian Cordillera during the post Middle Jurassic can be extended in south-central British Columbia as far back as the upper Paleozoic.

Geological and geochemical evidence for variable magmatism and tectonics in the southern Canadian Cordillera: Paleozoic to Jurassic suites, Greenwood, southern British Columbia

The Paleozoic and early Mesozoic rocks of the Greenwood mining camp in southern British Columbia are a part of the Quesnel terrane in the eastern part of the Intermontane Belt of the Canadian Cordillera. Upper Paleozoic rocks include the Knob Hill Group composed of oceanic tholeiitic basalts (with (La/Yb)n 0.4–1.2), associated with deep ocean sedimentary rocks and serpentinites; the Attwood Group that comprises island-arc tholeiites (with (La/Yb)n 1–4 and positive εNd values), clastic sedimentary rocks and limestones; and a unit of oceanic gabbros with (La/Yb)n < 0.5. These lithologically defined units occur as tectonically emplaced slivers of oceanic crust probably produced during the closure of the Slide Mountain basin during the Permian. They are unconformably overlain by Middle Triassic calc-alkaline volcanic and sedimentary rocks of the Brooklyn Group. The Brooklyn Group volcanic rocks have characteristics of mature island-arc rocks, including (La/Yb)n 2.5–4.5 and positive εNd values. The Paleozoic rocks are crosscut by a 200 million years old granodioritic intrusion containing zircon with an Early Proterozoic inheritance age (~2.4 Ga). By inference, southern Quesnellia may have been well offshore from the ancestral North American margin in the Mississippian, in close proximity to the margin by the Middle Triassic, and contiguous with it by the Early Jurassic. It is suggested that the complex tectonic history of extension and contraction of the southern Canadian Cordillera during the post Middle Jurassic can be extended in south-central British Columbia as far back as the upper Paleozoic.

Lithostratigraphy and limiting optical ages of the Pleistocene fill in Fraser River valley near Clinton, south-central British Columbia

Lithostratigraphy and limiting optical ages of the Pleistocene fill in Fraser River valley near Clinton, south-central British Columbia

SMALL MAMMALS AND STAND STRUCTURE IN YOUNG PINE, SEED-TREE, AND OLD-GROWTH FOREST, SOUTHWEST CANADA

Alternative silvicultural systems to clearcutting are receiving considerable attention in Pacific Northwest forests of North America. Understanding the implications of these harvesting systems on stand structure and biodiversity through time is a fundamental aspect of forest ecosystem management. This study was designed to test the hypothesis that diversity of stand-structure attributes and forest floor small-mammal communities will increase from young pine to seed tree to old-growth forest. The study area was within mixed Douglas-fir (Pseudotsuga menziesii)–lodgepole pine (Pinus contorta) forests within the Montane Spruce biogeoclimatic zone near Summerland in south-central British Columbia, Canada. This retrospective study had three replicate stands each of 17-yr-old “young pine” (clear-cut harvested), “seed tree” composed of young pine with Douglas-fir seed trees, and uncut “old-growth” composed primarily of Douglas-fir and lodgepole pine. Stand-structure attributes (coniferous tree layers and understo...

USING RADIO TELEMETRY TO DESCRIBE THE FALL MIGRATION OF EARED GREBES

Eared Grebes (Podiceps nigricollis) marked with small radio-transmitters in 1995 and 1996 at a breeding site in south-central British Columbia, Canada, were subsequently detected in fall at Mono Lake (California) and Great Salt Lake (Utah). At least 50% of all marked birds were detected on Mono Lake, and data collected in mid-October suggested that this proportion was consistent across years. These observations largely confirm a fall migration pattern that had been previously based on leg-band returns. Radio-tracking also confirmed that some movement occurred between Mono Lake and Salton Sea. In terms of the number of marked birds detected, the internal antenna-type transmitter produced superior results over other (attachment) protocols but their short range (<2 km) means that they will be effective only at sites where the birds are both abundant and concentrated such as Mono Lake, Great Salt Lake, and Salton Sea.

Age Structure and Growth of the Tree-seedling Bank in Subalpine Spruce-fir Forests of South-central British Columbia

We examined the dynamics of the tree-seedling bank in old-growth, subalpine Picea engelmannii—Abies lasiocarpa forests in south-central British Columbia by collecting all individuals <1.3 m tall within belt transects at two sites (n = ca. 500 per site) and determining their height, basal diameter and age. Seedlings were up to 149 y old. Regressions showed that spruce 1-m tall averaged 65-y old and fir 92-y old. Age structures indicated that recruitment into the seedling bank was variable with time, but that individuals of both species occurred in almost all 5-y age classes. Regressions of height and diameter vs. age had high predictability and showed that spruce grew more rapidly than fir. Allometric (height/diameter) relationships differed significantly between species; spruce had a much greater height/diameter ratio than fir. Seedlings accumulate gradually and persist for long periods in the seedling bank, thus forming a large pool of individuals that can potentially respond to opening of the canopy.

Response of northwestern chipmunks (Tamias amoenus) to variable habitat structure in young lodgepole pine forest

This study was designed to test the hypothesis that large-scale habitat alteration by stand thinning over a range of densities would increase the abundance and related population dynamics of northwestern chipmunks (Tamias amoenus) in young lodgepole pine (Pinus contorta) forest. Replicate study areas were located near Penticton, Kamloops, and Prince George in south-central British Columbia, Canada. Each study area had three stands thinned to densities of approximately 500 (low), 1000 (medium), and 2000 (high) stems/ha, with an unthinned young pine stand and an old-growth pine stand for comparison. Chipmunk populations were sampled intensively in thinned stands from 1989 to 1991 and in the unthinned and old-growth stands from 1990 to 1991. Habitat structure was sampled in all stands in 1990. For herbs and shrubs, the crown volume index values were similar among stands; for trees, this index was lowest for the low-density stands, with the index for all three thinned stands being lower than that for the unthinned stands. Species diversity and the structural diversity of vegetation were similar among stands. The abundance of chipmunks was significantly higher in low-density than in high-density thinned stands at Penticton (1.3-1.9 times higher) and Prince George (2.4-3.8 times higher) but not at Kamloops. Chipmunks were less abundant in old-growth stands than in the other four treatment stands. Breeding performance and recruitment followed the same pattern as abundance. Chipmunk survival was generally similar among stands. There were heavier chipmunks in the low-density stands in some years at Penticton. Northwestern chipmunks appear to prefer "open" habitats generated by heavy thinning of young lodgepole pine stands. This result was achieved in three different forest ecological zones and may enhance the overall forest ecosystem.

Cyanolichen Distribution in Young Unmanaged Forests: A Dripzone Effect?

Abstract In young forests of humid south-central British Columbia, Lobaria pulmonaria and other epiphytic “cyanolichens” attain optimum development over the lower branches of conifers growing within the dripzone of Populus. To account for this, we propose the existence of a “dripzone effect”, in which nutrient-rich leachates from the upper branches of Populus enhance the pH of nearby conifers to the benefit of cyanolichen colonization. The dripzone effect is presumably most pronounced in stands located over nutrient-rich soils, in which Populus plays a pivotal role in the early establishment of nitrogen-fixing epiphytic cyanolichens. This phenomenon is assumed to be widespread, but it apparently leads to colonization of conifers by cyanolichens only in humid regions not subject to acid rain. Though the presence of cyanolichens on trees belonging to the Pinaceae is probably indicative of allochthonous nutrient enrichment wherever it occurs, we stress that the dripzone effect is only one of many mechanisms ...

Response of northwestern chipmunks (&lt;i&gt;Tamias amoenus&lt;/i&gt;) to variable habitat structure in young lodgepole pine forest

This study was designed to test the hypothesis that large-scale habitat alteration by stand thinning over a range of densities would increase the abundance and related population dynamics of northwestern chipmunks (Tamias amoenus) in young lodgepole pine (Pinus contorta) forest. Replicate study areas were located near Penticton, Kamloops, and Prince George in south-central British Columbia, Canada. Each study area had three stands thinned to densities of approximately 500 (low), 1000 (medium), and 2000 (high) stems/ha, with an unthinned young pine stand and an old-growth pine stand for comparison. Chipmunk populations were sampled intensively in thinned stands from 1989 to 1991 and in the unthinned and old-growth stands from 1990 to 1991. Habitat structure was sampled in all stands in 1990. For herbs and shrubs, the crown volume index values were similar among stands; for trees, this index was lowest for the low-density stands, with the index for all three thinned stands being lower than that for the unth...

Optical dating studies of postglacial aeolian deposits from the south-central interior of British Columbia, Canada

Tests of the validity of optical dating of the fine-grained (4–11 μm) component of aeolian deposits from six sites in south-central British Columbia, using 1.4 eV (infrared) excitation of potassium feldspars, were made making use of known-age tephra beds. At one site on the western side of the Fraser Valley, samples bracketing the Mazama (7.5–7.6 ka, cal. yrs.) and Bridge River tephras (2.3 ka, cal. yrs.) yielded optical ages in accordance with the known ages when a correction for thermal-transfer was used. The same method was applied to aeolian deposits on the Fraser Plateau, known to have been deposited between 14 and 2.3 ka (cal. yrs). The ages obtained from five samples, from four separate exposures spanning 10 km, varied from 30 to 94 ka, clearly indicating that this sediment was not exposed to sufficient sunlight prior to burial. As a result of a detailed investigation it is suggested that the reason is that some grains had been transported over short distances (<100 m) while shielded within carbonate-cemented clusters.

Lithostratigraphy and paleomagnetism of pre-Fraser glacial deposits in south-central British Columbia

Lithostratigraphic records spanning considerable parts of the Pleistocene were studied at three sites in south-central British Columbia. A sedimentary succession near Pavilion includes three distinctly different till units. While the surface till can be associated with the last glaciation (the Fraser Glaciation δ18O stage 2), the ages of the two older till units are presently unknown. However, optical dating of outwash silt resting on the oldest till indicates that this outwash unit and all the overlying units are younger than ~160 ka. In Big Bar Creek valley, about 50 km north of Pavilion, an aggradational sequence of indurated glaciofluvial sand, gravel, and till is exposed. A silt unit and a sand lens within an overlying till bed near the top of the section have reversed magnetization, indicating deposition prior to 780 ka, probably during the Matuyama chron. The Big Bar Creek sequence also includes glacio(?)fluvial sediments near the base that are normally magnetized, suggesting that they were deposited, at the latest, during the Jaramillo subchron (~1.0 Ma), but probably during the Gauss chron, before 2.6 Ma. Reversely magnetized glacio(?)fluvial gravel and sand also occur along Jesmond Road between the Marble Range and Edge Hills. These units give support for the development of at least one Cordilleran ice sheet in the Early Pleistocene or Late Pliocene.

Lithostratigraphy and paleomagnetism of pre-Fraser glacial deposits in south-central British Columbia

Lithostratigraphic records spanning considerable parts of the Pleistocene were studied at three sites in south-central British Columbia. A sedimentary succession near Pavilion includes three distinctly different till units. While the surface till can be associated with the last glaciation (the Fraser Glaciation δ18O stage 2), the ages of the two older till units are presently unknown. However, optical dating of outwash silt resting on the oldest till indicates that this outwash unit and all the overlying units are younger than ~160 ka. In Big Bar Creek valley, about 50 km north of Pavilion, an aggradational sequence of indurated glaciofluvial sand, gravel, and till is exposed. A silt unit and a sand lens within an overlying till bed near the top of the section have reversed magnetization, indicating deposition prior to 780 ka, probably during the Matuyama chron. The Big Bar Creek sequence also includes glacio(?)fluvial sediments near the base that are normally magnetized, suggesting that they were deposited, at the latest, during the Jaramillo subchron (~1.0 Ma), but probably during the Gauss chron, before 2.6 Ma. Reversely magnetized glacio(?)fluvial gravel and sand also occur along Jesmond Road between the Marble Range and Edge Hills. These units give support for the development of at least one Cordilleran ice sheet in the Early Pleistocene or Late Pliocene.