U.S. Geological Survey 2000 Version 2.0, Updated Feb, 2015 vector digital data Reston, Virginia U.S. Geological Survey https://water.usgs.gov/lookup/getspatial?snake_river_plain_aquifer_system U.S. Geological Survey 1996 online publication Hydrologic Atlas USGS HA-730-H Reston, VA U.S. Geological Survey https://pubs.usgs.gov/ha/ha730/ch_h/H-text8.html This data set represents the extent of the Snake River Plain aquifer system, which includes both the basaltic and basin-fill aquifers. This dataset does not represent the full extent of the basaltic and basin-fill aquifers aquifers. This data set represents the extent of the surficial aquifer within the Snake River aquifer system. This aquifer system is primarily located in Idaho. These data delineate the areal extent of the Snake River Plain aquifer system, which includes both the basaltic and basin-fill aquifers, as defined in the 'Ground Water Atlas of the United States' (U.S. Geological Survey HA 730). The scale of source material is 1:2,500,000 and these data are not intended for use at a larger scale. The Snake River Plain regional aquifer system underlies a large, crescent-shaped lowland that extends from near the western boundary of Yellowstone National Park in eastern Idaho to the Idaho-Oregon border where the Snake River enters Hells Canyon. The northern and southern boundaries of the Snake River Plain generally coincide with the contact between unconsolidated deposits or Pliocene and younger basaltic rocks in the lowland and older rocks in adjacent highlands. Early ground-water studies concentrated only on that part of the plain east of the Thousand Springs area and north of the Snake River, an area of about 9,600 square miles. A regional study, which was begun in 1979 by the U.S. Geological Survey, focused on the entire 15,600 square miles of the Snake River Plain. During 1980, about 3.1 million acres on the plain was irrigated-about 2 million acres with surface water, about 1 million acres with ground water, and about 100,000 acres with a combination of surface and ground water. About 5,300 wells provided ground water for irrigation. Abrupt changes in hydrogeologic conditions along the Snake River between Salmon Falls Creek and King Hill, Idaho, make it feasible to discuss the regional aquifer system by area-the eastern and the western plains. In the eastern plain, the regional aquifer system consists primarily of Pliocene and younger basaltic rocks with some overlying and interbedded unconsolidated deposits; in the western plain, the aquifer system consists primarily of unconsolidated deposits with some Pliocene and younger basaltic rocks. The Pliocene and younger basaltic rocks are from 1,000 to 2,000 feet thick in large areas of the eastern plain but are that thick in only a small part of the western plain. Similarly, the saturated thickness of Pliocene and younger basaltic rocks is from 500 to greater than 1,000 feet in large areas of the eastern plain but is that thick in only a small part of the western plain. Because there are few deep wells in the eastern plain, the thickness of Pliocene and younger basaltic rocks in areas where these rocks range from 1,000 to more than 3,000 feet thick was estimated by using electrical resistivity surveys (the maximum thickness estimated was 5,500 feet). Consequently, some older volcanic rocks (including basalt and silicic volcanic rocks) might be included with Pliocene and younger basaltic rocks, particularly in areas where the thickness exceeds 1,000 feet. This is also true where the Pliocene and younger basaltic rocks are shown as thin (less than 100 feet thick) or absent along the north-central and northeastern margins of the plain. The aggregate thickness of unconsolidated deposits-those overlying, interbedded with, and underlying Pliocene and younger basaltic rocks was determined primarily from drillers' logs. The unconsolidated deposits have a thickness pattern opposite that of the Pliocene and younger basaltic rocks; the unconsolidated deposits are much thicker in the western plain than in the eastern plain and are as much as about 5,500 feet thick near the northwestern tip of the western plain. In the central part of the eastern and western plains, most wells penetrate only the upper part of the Pliocene and younger basaltic rocks. In these areas, therefore, the thickness of the unconsolidated deposits primarily represents deposits that overlie the Pliocene and younger basaltic rocks; much of this thickness represents soil that has developed on the Pliocene and younger basaltic rocks. In some places, such as parts of Craters of the Moon National Monument, virtually no soil has developed on the youngest basaltic rocks that were extruded only about 2,000 years ago. The topography of the volcanic rock surface underlying the uppermost unconsolidated deposits is indicated by figure 57, which shows the depth to the uppermost volcanic rocks. Pliocene and younger basaltic rocks are the shallowest volcanic rocks throughout much of the entire Snake River Plain. Miocene basaltic rocks and silicic volcanic rocks are the shallowest volcanic rocks, primarily near the margins of the eastern plain and in the southern and northwestern parts of the western plain. The canyonlike troughs in the volcanic rock surface in the western plain are the result of the complete erosion of near-surface, thin layers (generally less than 100 feet thick) of Pliocene and younger basaltic rocks that once overlaid thick sequences of unconsolidated deposits. The configuration of the regional water table of the aquifer system generally parallels the configuration of the land surface of the Snake River Plain; that is, the altitude of the water table is greatest in the extreme eastern part of the plain and is least in the Hells Canyon area along the Idaho-Oregon border. Upstream bending of the water-table contours where they cross the Snake River shows the places where the aquifer system is discharging to the river. The water-table contours shown in figure 58 were based on water levels measured in about 1,600 wells during spring 1980. In a general way, the configuration of and the spacing between contours indicate changes in the geologic and hydrologic character of the aquifer system and show the direction of horizontal ground-water movement at the water table. The increasing space between contours generally indicates more permeable or thicker parts of the aquifer. Conversely, the narrowing space indicates less permeable or thinner parts of the aquifer. Hydraulic head must increase to move the same volume of water through the less permeable or thinner parts of the aquifer system. Estimates of the depth to the regional water table can be made by subtracting the altitude of a water-table contour at a given point from the altitude of the land surface at the same point. Areas where shallow local aquifers or perched water bodies overlie the regional aquifer system are shown in figure 58. Water levels in these areas are higher than those in the regional aquifer system. Other such areas might exist but are too small to show in figure 58. These areas are underlain by rocks that have extremely low permeability. The juxtaposition of regionally mapped aquifers has led to some instances where an aquifer outcrop or shallow subcrop is bounded by a State line. This is a result of the regional mapping and national categorization methods used and is not meant to imply a hydrogeologic change coincident with a State boundary. Comments regarding the names of aquifers or the hydrogeologic interpretation of the aquifers can be directed to the U.S. Geological Survey, Water Mission Area, Office of Ground Water, https://water.usgs.gov/ogw/. The nationwide principal aquifers map, cited as a complete or partial source, refers to both a dataset published at 1:2,500,000 and a derived map printed at 1:5,000,000. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this Federal Geographic Data Committee-compliant metadata file is intended to document the data set in nonproprietary form, as well as in ARC/INFO format, this metadata file may include some ARC/INFO-specific terminology. 1998 publication date complete As needed -116.589954 -111.757914 45.052683 41.906777 USGS Thesaurus inlandWaters aquifer aquifer extent groundwater ISO 19115 Topic Category geoscientificInformation inlandWaters environment USGS Metadata Identifier USGS:45c220f9-60be-4380-9c82-6e967c293df4 Geographic Names Information System Idaho eastern Idaho Snake River None. Acknowledgement of the U.S. Geological Survey would be appreciated in products derived from these data. These data are not to be used at scales greater than 1:2,500,000. Selection of the aquifer polygon may also result in selection of non-aquifer polygons (AQ_CODE=999) within the aquifer extent. U.S. Geological Survey Water Webserver Team mailing address

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Reston VA 20192 USA 1-888-275-8747 h2oteam@usgs.gov Please use email. https://water.usgs.gov/GIS/browse/H053.jpg Image of the Snake River Plain Aquifer System .jpg Please recognize the U.S. Geological Survey (USGS) for use of this data. None Unclassified None Windows NT Version 4.0 (Build 1381) Service Pack 6; ESRI ArcInfo 8.1.0.415 U.S. Geological Survey 1999 map Principal aquifers of the United States (modified from Principal Aquifers, U.S. Geological Survey, 2003). National Atlas product Reston, VA U.S. Geological Survey https://water.usgs.gov/GIS/dsdl/USAaquiferMAP11_17.pdf U.S. Geological Survey 1989 map Hydrologic Investigations Atlas HA 730 Reston, VA U.S. Geological Survey https://pubs.usgs.gov/ha/ha730/index.html Source data was checked using standard USGS review procedures. Attributes were checked by plotting the coverage and reselecting for the different values. Polygon and chain-=node topology present. Every polygon has a label. This was checked using the labelerror command and the idedit command. The extent is based on the best available printed sources on the subject of aquifer extents. There is the potential that better data is available at the local level. All digitized lines when plotted at 0.05" were within the lineweight of the compilation source. U.S. Geological Survey 2000 online publication Hydrologic Atlas HA 730-H, fig. 53 Reston, VA U.S. Geological Survey https://pubs.usgs.gov/ha/730h/report.pdf 2500000 mylar separates 1996 currentness text aquifer reference Source provided location of aquifer extent line U.S. Geological Survey 2003 data USGS Groundwater Information Principal aquifers of the United States (modified from Principal Aquifers, U.S. Geological Survey, 2003) Reston, VA U.S. Geological Survey https://water.usgs.gov/ogw/aquifer/map.html 2500000 digital file 1992 currentness text Evaluate aquifer boundary Source provided location of aquifer extent line U.S. Geological Survey 1999 publication Reston, VA U.S. Geological Survey https://water.usgs.gov/ogw/aquiferbasics/volcan.html 2000000 digital file 1995 1999 ground condition Evaluate aquifer boundary Boundary used to delineate coastal extent of aquifer a.) Aquifer names and all or part of the outcrop line shown on the Nationwide 'Principal Aquifer' map (Miller, James A., 1998), were used with the extent of each aquifer from the various chapters of the 'Ground Water Atlas of the United States' to create this coverage. The largest scale map source available was used. Where the line defining the aquifer extent is the same as the outcrop, the data were copied from the Principal Aquifers data set. Otherwise data were traced from 1:7,500,000, 1:5,000,000, or 1:2,500,000 scale map sources onto a stable base material. Where the extent was defined by a state boundary or coastline, a standard USGS digital base of the same scale state boundary or coastline was used as the source. (The following steps were done using ARC/INFO 7.2.1 on Data General AViiON UNIX. Much of the terminology used will be specific to ARC/INFO). b.) The aquifer extent lines were digitized into ARCEDIT using standard USGStolerances. After digitizing, a check plot was created and reviewed against the traced map. If a line was located more than a line weight (0.05") from the digitized source, it was corrected during an ARCEDIT session. c.) Using the TRANSFORM command, the coverage containing the digitized, aquifer extent lines was combined with the coverage containing registration tics, was rubbersheeted from geographic to Albers Equal-Area Conic projection. An RMS error of less than 0.004 was accepted. If it was greater than 0.004 the location and values of the lat/long points were verified. Following this transformation, any aquifer lines from the aquifer extent coverage coincidental to aquifer lines from the 'Principal Aquifers' map data set were copied from the 'Principal Aquifers' map data set and put into the aquifer extent coverage. The aquifer extent coverage was cleaned, the topology was built, and labels were added. d.) Four items were added to the .PAT file: AQ_NAME (60 65 C) AQ_CODE (4 5 I), ROCK_NAME (40 45 C), ROCK_TYPE (4 5 I). ROCK_NAME comes from the Principal Aquifers Data set, 1998. The first digit of the three digit aq_code, refers to aquifer lithology. 100 series are numbers for unconsolidated sand and gravel aquifers 200 series are numbers for semiconsolidated sand aquifers 300 series are numbers for sandstone aquifers 400 series are numbers for carbonate-rock aquifers 500 series are numbers for sandstone and carbonate-rock aquifers 600 series are numbers for volcanic-rock aquifers 999 is given for non aquifer islands inside aquifer polygons e.) The following items were verified: --Digitizing RMS error (below 0.005) --Transformation RMS error (below 0.004) --Arcs match the traced mylar (no gaps between the plot and the compilation) --Arc and polygon topology exists --Coverage has a coordinate system defined --Attributes aq_name and aq_code have been added and populated correctly --Necessary files exist to redo any step 19970331 This step was done on an NT workstation. After plotting the extent at 1:2,000,000, the lines were checked with the documented sources. If needed, the lines were corrected to better represent the source data. This process may have included one or more of the following steps: --Reshaping the arc --Replacing the arc from the outcrop data, --Digitizing new lines polygons --Deleting polygons. 19991118 Due to a computer problem final corrected files were lost, however hard copy plots of those files were retained. This file was recreated from those plots using a similar process to that described above. Where extent lines were equal to the outcrop, data were extracted from the Principal Aquifers Data Set. Otherwise data were digitized from the retained hard copy plots using the same tolerances and software described above. A check plot was created and compared to the hard copy plot. Significant deviations, greater than approximately a line weight (0.005"), were corrected using ARCEDIT. Data were reviewed internally to assure compliance with original sources. 20000712 First draft of metadata created by J.M. Watermolen using FGDCMETA.AML ver.1.32 01/11/99 on ARC/INFO data set. 19991118 Documentation edited by S.M. Last, based on informal reviews. 20000107 Documentation updated by J.J. Skalet based on internal reviews. 20010504 Documentation, new data formats and metadata were updated and made available by Michael Ierardi. 20140202 Vector Complete chain 7 Entity point 1 GT-polygon composed of chains 1 Point 4 Albers Conical Equal Area 29.500000 45.500000 -96.000000 23.00000 0.000000 0.000000 coordinate pair 0.001024 0.001024 meters North American Datum of 1983 Geodetic Reference System 80 6378137.000000 298.257222 SNAKE_EXT.AAT Line attributes U.S. Geological Survey LNTYPE The line category U.S. Geological Survey 1 coastline or international boundary U.S. Geological Survey 2 interior aquifer contact line U.S. Geological Survey SNAKE_EXT.PAT Polygon attributes U.S. Geological Survey ROCK_NAME General lithology of the rocks that make up the aquifer Principal Aquifers Data set, 1998 Snake River Plain Aquifer system Principal Aquifers Data set, 1998 ROCK_TYPE Code for rock name Principal Aquifers Data set, 1998 600 Snake River Plain Aquifer system Principal Aquifers Data set, 1998 AQ_NAME Name of the aquifer Principal Aquifers Data set, 1998 Basalt and other volcanic-rock aquifers Principal Aquifers Data set, 1998 AQ_CODE Numeric code for a particular aquifer Derived to help manage the data when numerous aquifers are aggregated 606 Basalt and other volcanic-rock aquifers Principal Aquifers Data set, 1998 999 Code for aquifer absent Principal Aquifers Data set, 1998 The original aquifer data was compiled in arc/info coverage format. This data has been updated to GIS shape and Geo Data Base format for increased useability. 1.) Principal Aquifers of the 48 Conterminous United States, Hawaii, Puerto Rico, and the U.S. Virgin Islands available at https://water.usgs.gov/lookup/getspatial?aquifers_us 2.) Ground Water Atlas of the United States Hydrologic Investigations Atlas HA 730 available at https://pubs.usgs.gov/ha/ha730/ U.S. Geological Survey Michael Ierardi mailing and physical address

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Reston VA 20192 USA (800) 426-9000 mierardi@usgs.gov Although these data have been used by the U.S. Geological Survey, U.S. Department of the Interior, no warranty expressed or implied is made by the U.S. Geological Survey as to the accuracy of the data. The act of distribution shall not constitue any such warranty, and no responsibility is assumed by the U.S. Geological Survey in the use of this data, software, or related materials. Shape Online accessible data WinZip compressed file 0.26 https://water.usgs.gov/GIS/dsdl/snake_river_shp.zip GeoDataBase Online accessible data WinZip compressed file 0.43 https://water.usgs.gov/GIS/dsdl/snake_river_aquifer_system_gdb.zip ARC export Online accessible data WinZip compressed file 0.31 https://water.usgs.gov/GIS/dsdl/snake_aq_cov.zip None. This dataset is provided by USGS as a public service. 20201117 U.S. Geological Survey Ask USGS -- Water Webserver Team mailing

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Reston VA 20192 1-888-275-8747 (1-888-ASK-USGS) mierardi@usgs.gov FGDC Content Standards for Digital Geospatial Metadata FGDC-STD-001-1998