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The Itcha Range, also known as the Itchas, is a small isolated mountain range in the West-Central Interior of British Columbia, Canada. It is located northeast of the community of Anahim Lake. With a maximum elevation of , it is the lowest of three mountain ranges on the Chilcotin Plateau extending east from the Coast Mountains. Two mountains are named in the Itcha Range; Mount Downton and Itcha Mountain. A large provincial park surrounds the Itcha Range and other features in its vicinity. More than 15 animal species are known to exist in the Itcha Range area, as well as a grassland community that is limited only to this location of British Columbia. The Itcha Range is within territory which has been occupied by aboriginal peoples for millennia. This area has a relatively dry environment compared to the Coast Mountains in the west.
In contrast to most mountain ranges in British Columbia, the Itcha Range represents an inactive shield volcano. This highly dissected volcanic edifice consists of a variety of rock types, including basanite, hawaiite, trachyte, rhyolite, phonolite and alkali olivine basalt. They were deposited by different types of volcanic eruptions characterized by passive lava flows and explosivity. Two stages of eruptive activity have been identified at the volcano along with three sub-phases that are limited only to the first stage of development. The main body of the Itcha Range is between 3.8 and 3.0 million years old and thus over two million years ago it passed the most active shield stage of life. A period of dormancy lasting for almost a million years followed, which was interrupted by the post-shield stage of volcanism 2.2 to 0.8 million years ago. More recent volcanic activity in and around the Itcha Range might have occurred in the last 340,000 years to produce .
The Itcha Range is part of an east–west trending volcanic zone called the Anahim Volcanic Belt. This consists of large shield volcanoes, small cinder cones, and lava flows that become progressively younger from west to east. Several explanations have been made regarding the creation of this feature, each citing a different geologic process. If volcanic activity were to resume at the Itcha Range, Canada's Interagency Volcanic Event Notification Plan (IVENP) is prepared to notify people threatened by eruptions.
Stream erosion has played a significant role in dissecting the mountain range, and many of its peaks are dotted with . This dissection has resulted in a variety of , such as , crags and domes. Small graveled creeks flow from alpine mountains out onto the regional prairies where there are pale blue rock-bottomed , including the so-named Itcha Lake.Richmond P. Hobson (2025). 9780771041709, National Library of Canada Cataloging in Publication. ISBN 9780771041709 Three streams drain the Itcha Range, namely Corkscrew Creek, Downton Creek and Shag Creek. Although the Itcha Range has been dissected by stream erosion and subsequently glaciated, its original shape has been largely preserved. Rocks in the Itcha Range are a variety of colours, including red, white and yellow.
In contrast to the Coast Mountains, the Interior Plateau experiences a precipitation peak in the summer months, reflecting the influence of summer convective storms, and most of winter precipitation falls as snow. The mean annual precipitation for the area ranges from about whereas the mean annual temperature is approximately , with a summer mean of and a winter mean of .
Several animal species inhabit around the Itcha Range. Among them are cougars, wolves, grizzly bears, black bears, moose, mule deers, mountain goats, beavers, coyotes, red foxes, muskrats, martens, river otters, lynx and wolverines. Also present is the largest herd of woodland caribou in southern British Columbia, as well as the most northerly population of California bighorn sheep in North America.
The Anahim hotspot is underlain by a low-velocity anomaly that extends approximately into the mantle north of the Juan de Fuca slab. However, this low-velocity anomaly may extend deeper southward beneath the Juan de Fuca slab. Coupled with the well documented temporal progression of surface volcanism, this has led to the conclusion that the Anahim hotspot is supplied by a mantle plume over slab edge flow. A small high-velocity anomaly east of Nazko Cone marks the eastern extent of the Anahim hotspot track.
Magmatism in the Anahim Volcanic Belt can be traced as far back as 10–14 million years ago with the emplacement of and as well as the eruption of rhyolite flows and breccias on the British Columbia Coast. The slow continuous westward motion of the North American Plate during the late Neogene positioned the Anahim hotspot further east at the Chilcotin Plateau where volcanic activity built the Rainbow Range shield volcano 8.7 to 6.7 million years ago. Volcanism then shifted eastwards, in displacement contrary with the North American Plate's movement, 6.1 million years ago to construct the Ilgachuz Range shield volcano. Renewed volcanic activity southeast of the Ilgachuz Range starting 3.5 million years ago led to the creation of the Itcha Range, the youngest of the three Anahim shield volcanoes. The Itcha Range continued to be an area of Anahim hotspot volcanism well into the Quaternary period (2.58 million years ago to present).
With a maximum elevation of , the Itcha Range is the lowest of the three Anahim shield volcanoes. Its highest point is Mount Downton, which is situated in the middle of the shield. Just to the northeast is Itcha Mountain, the second highest peak with an elevation of . These peaks are situated on top of the shield, which has a topographic prominence of about .
The Itcha Range has a broad, gently sloping structure typical of shield volcanoes. It is mainly composed of thick felsic lava flows that were erupted from a central vent. These are overlain by thick mafic alkaline lava flows and at least 30 small cinder cones. Hawaiite is the dominant rock type, but alkali olivine basalt and spinel lherzolite-bearing basanite is also present. They merge laterally with lavas of the much older Chilcotin Group, which surrounds the Anahim Volcanic Belt. However, the exact nature of the relationship between the Anahim Volcanic Belt and the Chilcotin Group is unknown.
Exposed in the middle of the mountain range is an assemblage of deformed andesite to dacite lava flows and volcanoclastic sediments. These basement rocks were created during the late Mesozoic era, long before the Itcha Range formed. They are similar to rocks found in the Hazelton Group, situated north of the Itcha Range, and the Ootsa Lake Group of the Intermontane Belt.
A 900,000‑year‑long period of quiescence followed after the felsic shield-building stage, during which time erosion ate away at the shield's gentle slopes. This quiescence was followed by a mafic capping stage between 2.2 and 0.8 million years ago, but renewed activity might have occurred in the last 340,000 years. Alkali olivine basalts of the mafic capping stage were derived from the fractionation of a clinopyroxene, olivine and oxide assemblage. However, the associated hawaiite lavas may have derived from an alkali olivine basalt parent by the fractionation of a clinopyroxene-dominated assemblage at higher pressures. As volcanic activity waned during the mafic capping stage, lava flows became more viscous and decreased in volume. This suggests that parental magmas may have been derived by increasingly smaller degrees of partial melting with time. If volcanic activity of the Itcha Range is related to a hotspot, this temporal and spatial evolution would suggest a waning heat source.
The main body of the shield erupted over an area of about . Volcanic activity associated with the Itcha Range extended south to the Satah Mountain area where lavas erupted along a north-northwest trending fault system and covered an additional area of . Although the Satah Mountain volcanic field is not part of the Itcha Range, it is linked to the range by a volcanic ridge. (1994). 9780612000841, McGill University. ISBN 9780612000841
After the basal trachytes were erupted, the explosive phase produced alkali-feldspar porphyritic trachytes, which erupted as pyroclastic deposits with minor, small lava flows and domes. The explosive eruptions produced pumice flows, bedded tuffs, , reworked polymict debris flows and lava flows less than thick. The porphyritic trachytes erupted at the summit of the shield and flowed towards the northeast and east. Because the porphyritic pyroclastic deposits are buried by younger volcanic rocks and glacial drift deposits, the maximum thickness of them is unknown.
The felsic shield-building stage ended with the post-explosive phase. This phase of activity created small , lava flows, minor , channelized debris flows and a few glassy dikes at the summit of the shield volcano. These consist of alkali-feldspar porphyritic quartz-trachyte and trachyte. Alkali-feldspar quartz-trachyte plugs formed in rhyolites and trachytes of the pre-explosive phase, as well as pyroclastic deposits and feldspar trachyte lava flows of the explosive phase. Later activity produced trachyte and phonolite plugs and lava flows. This volcanism occurred mainly at the shield's summit and on its western flank. Massive lava flows from this volcanic activity have a thickness of about whereas three successive lava flows at the summit have a combined thickness of more than . Lava from the western flank flowed over basement rocks and trachytes of the pre-explosive phase. In contrast, lava from the summit flowed over and lava flows of the explosive phase. Mount Downton and Itcha Mountain were formed during this eruptive period. The final volcanic event of the post-explosive phase produced thick trachyte lava flows on the western flank.
Volcanism of the mafic capping stage began with the eruption of aphyric hawaiite lava flows. These were extrusive from dikes and dissected cinder cones in the central and southeastern parts of the Itcha Range. Alkali olivine basalts were erupted contemporaneously from younger better preserved cinder cones and form lava flows reaching thick. Once the alkali olivine basalt flows cooled, they formed well-developed columnar joints. Feldspar-phyric, highly vesiculated hawaiites and were later erupted from several vents on the summit of Itcha Mountain.
In the northwestern and northeastern parts of the shield volcano, basanite lava flows were erupted and are volumetrically subordinate. These represent the youngest known lavas of the Itcha Range. However, a cinder cone in the middle of the shield could be much younger, perhaps as young as the basanites at Nazko Cone to the east, which were erupted 340,000 to 7,100 years ago. The older basanites in the Itcha Range may have been erupted contemporaneously with the late feldspar hawaiites.
Mount Downton was named by D. M. MacKay, a member of the British Columbia Land Surveyors (BCLS) who conducted topography surveys in the area. He named it after Geoffrey M. Downton, another BCLS member who is credited for first noting the hydroelectric potential inherent in the elevation differential between the Bridge River and Seton Lake on opposing sides of Mission Ridge above Shalalth in December 1912. This name for the mountain was adopted on February 7, 1947. The name Itcha Mountain was adopted on March 4, 1954, for the range's second highest peak.
Settlers arrived in the area from Bella Coola in the early 1900s to establish . One particular ranch, the Home Ranch, used the Blackwater Trail between the Ilgachuz and Itcha ranges to carry supplies and cattle to be sold at cattle sales in the small city of Quesnel. Remains of this ranch are still present, as well as many trails that were used as supply routes.
The Itcha Range and the surrounding area were designated as a Class A provincial park in 1995 to protect the alpine grasslands, and wildlife habitats. This protected area was named Itcha Ilgachuz Provincial Park after the Itcha and Ilgachuz ranges, the latter of which is also in the park.
Because of the remote location of the Itcha Range, future eruptions are not a major hazard. Future volcanism is most likely in the form of basaltic cinder cones, but eruptions of felsic magma can not be ruled out. The most immediate hazard relating to future eruptions is of local concern only and includes the possibility of forest fires by lava flows and the disruption of local air traffic if an eruption column is produced. Volcanic ash reduces visibility and can cause jet engine failure, as well as damage to other aircraft systems.
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