Geology and Hydrology of
Genevieve Atwood, October 2007
Chief Education Officer, Earth Science Education
To view this talk on the web, go to http://www.earthscienceeducation.org/ and follow the links.
The purpose of this talk is to give some perspective, some rationale of why Salt Lake County’s watersheds are the way they are, specifically why Great Salt Lake is located where it is; why the Jordan River flows north; why some places are better than others for landfills; and how climate has affected the region.
Here are three take-away messages about
Geology 101, Earth materials: The bedrock of
Geology 101, Landscapes: Tectonics sets the scene.
Erosion and deposition modify the scene. Extensional tectonics of the past 20
million years has caused
Hydrology 101: Ground water and surface what of
FIRST – location, location, location.
LINK to USGS Tech Pub 31 map of major drainages in
LINK to USGS Tech Pub 31 map of
LINK to PRWUA - JVWCD Map of watersheds of Salt Lake County
What this means to
With respect to watersheds:
· Colorado Plateau = rivers run through it;
· Basin and Range = rivers run to it.
http://220.127.116.11/utah_panorama_atlas/page20/files/page20-1021-full.html used with permission William Bowen, 2006. SLCo-page20-1021
Rocky Mountain region = high terrain with massive complexes of mountains and ranges above 9,000 ft a.s.l.; humid continental – hot summer climate, more precipitation than evaporation; snow in winter; recharge from snow melt; vegetated valleys and parks; extensive watershed catchment areas; major recharge areas for Salt Lake Valley aquifers; major sources of ground and surface water for Salt Lake County communities; water quality – naturally good quality although affected by geology, issues of mining, non-point sources, and point sources; evidence of both erosion and deposition processes; issues of climate change.
Basin and Range physiographic province
Bounded by Wasatch fault on the east; broad basins and narrow, north-south trending mountain ranges; arid to semi-arid climate; climate zone = steppe (less precipitation than evaporation); limited precipitation; ephemeral drainages from ranges, winter snow with some recharge; thunderstorms cause rapid runoff and debris flows; limited as ground water sources for Salt Lake County (Magna, Herriman?, Kennecott properties?); water quality issues affected by geology, residence time, mining; erosion in ranges but region dominated by deposition in broad; closed basins, issues of climate change.
LINK – UGS(Stantec) geologic units of SLCounty – affects water quality and water flow
SECOND – Tectonics and landforms
Why are there contrasting physiographic provinces? Different geologic histories.
LINK to schematic of extension of Basin and Range
Basin and Range physiographic province = extensional tectonics.
THIRD – Climate change
Given that tectonics results in closed-basins, we get
lakes. Closed basin lakes are historians of climate change. As colder, wetter,
cloudier climate drives the lake upward (1) wave processes create shoreline
expressions, and (2) rivers carry sediments and dissolved constituents into the
lake and they are deposited as layers across the lake bed. Note: these layers
are important to
LINK Great Salt Lake –
LINK to USGS Tech Pub 31 – SLCounty precipitation
FOURTH – ground and surface water hydrology of SLCounty.
Analysis of the Arnow, 1983 (USGS Tech Pub 31) – Thiros, 2003 (USGS WRI-034325) schematics
LINK to schematic in color (Thiros, 2003)
LINK to schematic in black and white (Arnow, 1983)
LINK to summary of ground water and surface water relationships