Editing Basin, Montana (section)

== Geography and geology ==
Basin, in [[Jefferson County, Montana|Jefferson County]], is part of the Helena [[Helena, Montana micropolitan area|Micropolitan Statistical Area]].<ref>{{cite web|title=OMB Bulletin No. 10-02|url=https://obamawhitehouse.archives.gov/sites/default/files/omb/assets/bulletins/b10-02.pdf|publisher=Executive Office of Management and Budget|date=December 1, 2009|page=74|access-date=September 1, 2013|url-status=live|archive-url=https://web.archive.org/web/20170121004722/https://obamawhitehouse.archives.gov/sites/default/files/omb/assets/bulletins/b10-02.pdf|archive-date=January 21, 2017}}</ref> It lies at an elevation of {{convert|5364|ft|m|0}} above sea level<ref name="gnis"/> along [[Interstate 15 in Montana|Interstate 15]] about {{convert|30|mi}} by road north of [[Butte, Montana|Butte]] and {{convert|38|mi}} south of [[Helena, Montana|Helena]] in a narrow canyon.<ref>{{cite web| url=https://www.google.com/maps/place/Basin,+MT/@46.2810949,-112.3266278,13z/data=!3m1!4b1!4m5!3m4!1s0x535b4222b57ed681:0xd4b54266573df2cc!8m2!3d46.2713177!4d-112.2636205!5m1!1e4| title = Basin, MT |website = Google Maps |access-date=August 21, 2018}}</ref> The community is largely surrounded by the [[Beaverhead-Deerlodge National Forest]].<ref name="Montana Atlas"/> Basin Creek flows south through the center of Basin to its confluence with a larger stream, the [[Boulder River (southwestern Montana)|Boulder River]], which flows east along the south side of Basin.<ref name="Montana Atlas">{{cite book|title=Montana Atlas & Gazetteer|publisher=DeLorme|location=Yarmouth, Maine|pages=38&ndash;39|year=2007|edition=6th|isbn=978-0-89933-339-7}}</ref> No paved roads except the interstate highway, which runs along the river canyon, connect Basin to other towns.<ref name="Montana Atlas"/> About {{convert|10|mi|km|0}} upstream on Basin Creek lies the [[Continental Divide]].<ref name="Montana Atlas"/> According to the United States Census Bureau, the CDP has a total area of {{convert|33.0|km2|order=flip}}, all land.<ref name="Census 2010"/>

In the late [[Cretaceous]] (roughly 81 to 74 million years ago), molten rock ([[magma]]) rose to the Earth's surface in and near what later became Jefferson County and eventually formed an intrusive body of granitic rock up to {{convert|10|mi|km|0}} thick and {{convert|100|mi|km|0}} in diameter. This body, known as the [[Boulder Batholith]], extends from Helena to Butte, and is the host rock for the many valuable ores mined in the region. As the granite cooled, it cracked, and hot solutions infiltrated the cracks to form mineral [[vein (geology)|veins]] bearing gold and other metals. Millions of years later, weathering allowed gold in the veins to wash down to the gravels in Basin Creek, Cataract Creek, and the other creeks near Basin, as well as the Boulder River.<ref>{{cite web|title=Math and Science Initiative: Elkhorn Volcanoes and the Boulder Batholith |publisher=State of Montana, Office of Public Instruction |url=http://mathscience.mt.gov/Elkhorn.html |access-date=December 17, 2007 |archive-url=https://web.archive.org/web/20071226191413/http://mathscience.mt.gov/Elkhorn.html |archive-date=26 December 2007 |url-status=dead }}</ref>

The Basin area is underlain by the [[quartz monzonite]] of the Boulder Batholith. The batholith is overlain by [[dacite]] from the [[Paleogene]] and [[Neogene]] periods (roughly 66&nbsp;million to 1.8&nbsp;million years ago) and [[andesite]] from the late Cretaceous. The andesite and monzonite are cut by [[Dike (geology)|dikes]] of dacite and [[rhyolite]].<ref>{{cite web  | title = Historic Narratives, Boulder | publisher = Montana Government, Department of Environmental Quality |date=August 2004  | url =http://www.deq.state.mt.us/abandonedmines/linkdocs/techdocs/75tech.asp | access-date = December 17, 2007 |archive-url = https://web.archive.org/web/20040917174713/http://www.deq.state.mt.us/abandonedmines/linkdocs/techdocs/75tech.asp |archive-date = September 17, 2004|url-status=dead}}</ref>