The Mount Barr Plutonic Complex (MBPC) is a circular body of

intrusive rock Intrusive rock is formed when magma penetrates existing rock, crystallizes, and solidifies underground to form ''Igneous intrusion, intrusions'', such as batholiths, dike (geology), dikes, Sill (geology), sills, laccoliths, and volcanic necks.I ...

in the

Cascade Mountains The Cascade Range or Cascades is a major mountain range of western North America, extending from southern British Columbia through Washington and Oregon to Northern California. It includes both non-volcanic mountains, such as many of those in the ...

of southern

British Columbia British Columbia is the westernmost Provinces and territories of Canada, province of Canada. Situated in the Pacific Northwest between the Pacific Ocean and the Rocky Mountains, the province has a diverse geography, with rugged landscapes that ...

, Canada. It is located southwest of the

district municipality A district municipality is a designation for a class of municipalities found in several locations, including Canada, Lithuania, and South Africa. Canada British Columbia Under provincial law, municipalities in British Columbia are to be desi ...

Hope Hope is an optimistic state of mind that is based on an expectation of positive outcomes with respect to events and circumstances in one's own life, or the world at large. As a verb, Merriam-Webster defines ''hope'' as "to expect with confid ...

, centered around

Wahleach Lake Wahleach Lake, commonly known as Jones Lake, is a lake and reservoir located in the Skagit Range in the Lower Mainland of British Columbia, Canada, east of the city of Chilliwack, British Columbia, Chilliwack and southwest of the town of Hope, Brit ...

. The complex takes its name from Mount Barr, one of many

mountain A mountain is an elevated portion of the Earth's crust, generally with steep sides that show significant exposed bedrock. Although definitions vary, a mountain may differ from a plateau in having a limited summit area, and is usually higher t ...

s consisting of MBPC intrusive rocks. Three

granitoid A granitoid is a broad term referring to a diverse group of coarse-grained igneous rocks that are widely distributed across the globe, covering a significant portion of the Earth's exposed surface and constituting a large part of the continental ...

intrusions of

Miocene The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...

age comprise the MBPC. The largest intrusion consists of rocks ranging from

quartz diorite Quartz diorite is an igneous, plutonic ( intrusive) rock, of felsic composition, with phaneritic texture. Feldspar is present as plagioclase (typically oligoclase or andesine) with 10% or less potassium feldspar. Quartz is present at between 5 an ...

quartz monzonite Quartz monzonite is an intrusive, felsic, igneous rock that has an approximately equal proportion of orthoclase and plagioclase feldspars. It is typically a light colored phaneritic (coarse-grained) to porphyritic granitic rock. The plagioclase ...

and makes up 80% of the complex. Two younger

stocks Stocks are feet and hand restraining devices that were used as a form of corporal punishment and public humiliation. The use of stocks is seen as early as Ancient Greece, where they are described as being in use in Solon's law code. The law de ...

are situated within the main intrusion and consist of quartz monzonite.

K–Ar dating Potassium–argon dating, abbreviated K–Ar dating, is a radiometric dating method used in geochronology and archaeology. It is based on the measurement of the product of the radioactive decay of an isotope of potassium (K) into argon (Ar). Potas ...

of the MBPC has given ages ranging from 21 to 16 million years old.

References

Skagit Range Landforms of Lower Mainland Pemberton Volcanic Belt Stocks (geology) Miocene magmatism Igneous petrology of British Columbia Neogene British Columbia {{BritishColumbiaInterior-geo-stub