Editing Washington County, Arkansas (section)

===Geology===
Washington County sits on a [[basement]] of [[Precambrian]] [[granite]] and [[rhyolite]], as most of the continental interior of the [[United States]] does.<ref>{{cite book |title=Washington County History |last=Mathis |year=1989 |publisher=Shiloh Museum |location=Springdale, AR |page=9 }}</ref> Much of the county's geologic history must be inferred from nearby [[Oklahoma]] and [[Missouri]] research, due to the steepness of the more recently formed mountains that did not form in the neighboring states. This [[igneous]] material was eroded until the [[Paleozoic]], when oceans covered the now-low-lying area.<ref name="hwc1" >{{cite book |title=Washington County History |last=Mathis |year=1989 |publisher=Shiloh Museum |location=Springdale, AR |page=11 }}</ref> These oceans came and retreated for 300 million years, depositing various different sediments during that time. This created [[fossiliferous]] [[limestone]] and [[Ripple marks|ripple marked]]-[[sandstone]], both present throughout the north part of the county as evidence of ancient oceans.<ref name="hwc1" />

Sediments were deposited from the [[Devonian]], [[Mississippian age|Mississippian]], and [[Pennsylvanian (geology)|Pennsylvanian]] periods. During this deposition period, the county had a climate similar to that of the present-day [[The Bahamas|Bahamas]], as the [[equator]] was north of Washington County.<ref>{{cite book |title=Washington County History |last=Mathis |year=1989 |publisher=Shiloh Museum |location=Springdale, AR |page=14 }}</ref> The Devonian brought mostly [[shale]]s, the Mississippian brought the [[limestone]]s and [[chert]] visible in the bluffs. This chert is present throughout most of the county. The county is also home to the Boone Formation (red soils), white limestones, the [[Wedington, Arkansas|Wedington]] Sandstone, the [[Batesville, Arkansas|Bastesville]] Sandstone, the [[Pitkin Corner, Arkansas|Pitkin]] formation (ocean-fossil limestone), and the [[Fayetteville Shale]].

Settlers were attracted to the area by its numerous streams, used to power [[gristmill]]s, [[sandstone]]s and [[clay]]s for use in construction, [[Agricultural lime|lime]]-sweetened soil, and chert for road construction.<ref>{{cite book |title=Washington County History |last=Mathis |year=1989 |publisher=Shiloh Museum |location=Springdale, AR |page=2 }}</ref>

Today, Washington County consists of two main formations, the [[Boston Mountains]] and the Springfield Plateau. During the late [[Pennsylvanian (geology)|Pennsylvanian]], [[sediment]]s were deposited on top of the Springfield Plateau. The area was uplifted during the [[Ouachita orogeny]] and subsequent erosion formed the rugged Boston Mountains. Erosion of these sediments causes the Boston Mountains to be carved steeply in the south, while in the north of the county, the Boston Mountain sediments are almost entirely eroded, exposing the older rocks of the Springfield Plateau.