Park County Geology & Groundwater Resources Study

OF-15-11 Geology and Groundwater Resources of Park County


Barkmann, P.E., Sebol, L.A., Fitzgerald, F.S., and Curtiss, W.M., “Geology and Groundwater Resources of Park County”: Colorado Geological Survey, Open-File Report OF-15-11, revised 2017.

This open-file report is intended to provide a regional overview with the general public in mind, although it contains detailed background that may be beneficial to more technical users. This multiyear (2011-2016) project was made possible with multiple sources of funding, including grants from the Colorado Water Conservation Board (CWCB) as well as the Park County Land and Water Trust Fund (LWTF). The Colorado Geological Survey (CGS), through its Severance Tax and/or Colorado General Operational Funds, and CUSP have provided match.

Park County has experienced considerable population growth in recent decades with development becoming increasingly reliant on local groundwater resources. A diverse geologic setting characterizes the county and groundwater may be found in many of those settings. This product compiles the most recent geologic mapping and interpretations focusing on groundwater occurrences in the various geologic formations found in the area. The 2017 revision adds a discussion of groundwater types and quality, as presented in more detail below. This open-file report is intended to provide a regional overview with the general public in mind, although it contains detailed background that may be beneficial to more technical users.

Park County straddles two very different geologic terrains that share a long and complex history. The east side of the County extends into the Precambrian cored Front Range uplift of the Rocky Mountains. The west side of the County covers the South Park topographic basin, a 50 miles long by 35 miles wide structural feature shaped by a long and varied history of geologic processes. It contains a wide variety of crystalline igneous and metamorphic rocks, volcanic rocks, and sedimentary units, ranging in age from Precambrian through Cenozoic. Based on differences in hydrologic properties, aquifers and confining units in Park County can be grouped into three general categories: 1) crystalline-rock aquifers, 2) sedimentary bedrock aquifers and confining units, and 3) unconsolidated Quaternary deposits. Within these categories, there were 19 mapped hydrogeologic units.

There were 7,656 completed water wells in the Colorado Division of Water Resources database, inventoried in Park County as of December 19, 2012. Permitted uses include: domestic or household use only, livestock, commercial, industrial, municipal, irrigation, monitoring and other (such as evaporative, fire, geothermal, gravel, or unspecified). Wells and springs were assigned a hydrogeologic unit. Due to various sources of uncertainty, hydrogeologic unit designations were assigned a confidence level value of 1, 2, or 3, with 3 representing the least confidence.

A Park County groundwater quality database was compiled from publicly available databases, reports, and samples collected in 2011, 2012, 2014 and 2016 by the Coalition for the Upper South Platte (CUSP) with some assistance by CGS. The primary electronic data source was the Water Quality Portal (WQP) from the National Water Quality Monitoring Council. Groundwater data was also manually compiled from other publicly available publications not in the WQP. A total of 689 sample sites had groundwater quality data through 2016. A limited number of sample locations have data from multiple sampling events at the same well or spring. Data analysis for these locations used the maximum value detected, unless it was identified as an anomalous outlier. Where feasible, dissolved water quality data was used preferentially over total data.

Water quality in sampled Park County wells and springs is variable and dependent on local geology, geography, and seasonal influences. It is emphasized that the existing database spans a time period of multiple decades and the data do not represent a synoptic view of water quality conditions. The water quality database was evaluated for water type in each of the hydrogeologic units. Cations (sodium, potassium, calcium, and magnesium) and anions (chloride, bicarbonate, carbonate, and sulfate) data were used to generate Stiff diagrams and/or pie charts. Pie charts were scaled in size relative to the total dissolved solids (TDS) concentration, with larger pies having higher measured TDS. Additionally, groundwater quality was evaluated against the federal Environmental Protection Agency/Colorado maximum contaminant level (MCL) primary and secondary standards for drinking water. Constituents having primary and/or secondary MCL exceedances were mapped using circles of varying sizes that were blue for concentrations at or below the MCL and red if they exceeded the MCL. One or more exceedances of the primary MCLs were observed for fluoride, nitrate, arsenic, beryllium, lead, uranium, and gross alpha. Similarly, exceedances of the unenforceable secondary MCLs were noted for pH, total dissolved solids, chloride, fluoride, sulfate, aluminum, iron, manganese, and zinc. The most common constituents exceeding primary or secondary drinking water standards were manganese, sulfate, uranium, and gross alpha.

Available for download:

Report text with figures (does not include plates, which are listed individually below!)
ArcGIS shape files and layers are available as geodatabases, plus as a map package with ArcGIS 10.0+ compatibility.

List of Individual Plates (40×48″)

1. Geologic Map of Park County.
2. Cross-sections Through Park County.
3. Hydrogeologic Unit Map: Precambrian Crystalline Bedrock.
4. Hydrogeologic Unit Map: Tertiary and Cretaceous Intrusive and Volcanic Igneous Rocks.
5. Hydrogeologic Unit Map: Older Paleozoic Formations.
6. Hydrogeologic Unit Map: Belden Formation.
7. Hydrogeologic Unit Map: Minturn Formation.
8. Hydrogeologic Unit Map: Maroon Formation.
9. Hydrogeologic Unit Map: Garo Sandstone.
10. Hydrogeologic Unit Map: Morrison Formation.
11. Hydrogeologic Unit Map: Dakota Sandstone.
12. Hydrogeologic Unit Map: Benton/Niobrara.
13. Hydrogeologic Unit Map: Pierre Shale.
14. Hydrogeologic Unit Map: Laramie-Fox Hills Aquifer.
15. Hydrogeologic Unit Map: Laramide Sedimentary Units.
16. Hydrogeologic Unit Map: Tallahassee Creek Conglomerate.
17. Hydrogeologic Unit Map: Antero Formation.
18. Hydrogeologic Unit Map: Wagontongue-Trump Formation.
19. Hydrogeologic Unit Map: Unconsolidated Quaternary Deposits.
20. Water Quality Stiff Diagram Map: Countywide
21. Water Quality Pie Chart Map with TDS: Countywide
22. Water Quality Pie Chart Map With TDS: Precambrian Crystalline Bedrock
23. Water Quality Pie Chart Map with TDS: Tertiary Intrusive and Volcanic Rocks
24. Water Quality Pie Chart Map with TDS: Older Paleozoic Formations
25. Water Quality Pie Chart Map with TDS: Belden Formation
26. Water Quality Pie Chart Map with TDS: Minturn Formation
27. Water Quality Pie Chart Map with TDS: Maroon Formation
28. Water Quality Pie Chart Map with TDS: Garo Sandstone
29. Water Quality Pie Chart Map with TDS: Morrison Formation
30. Water Quality Pie Chart Map with TDS: Dakota Sandstone
31. Water Quality Pie Chart Map with TDS: Benton & Niobrara Formations
32. Water Quality Pie Chart Map with TDS: Pierre Shale
33. Water Quality Pie Chart Map with TDS: Laramie-Fox Hills Formations
34. Water Quality Pie Chart Map with TDS: Laramide Sedimentary Units
35. Water Quality Pie Chart Map with TDS: Tallahassee Creek Conglomerate
36. Water Quality Pie Chart Map with TDS: Antero Formation
37. Water Quality Pie Chart Map with TDS: Wagontongue-Trump Formation
38. Water Quality Pie Chart Map with TDS: Quaternary Deposits

GIS information

An ArcGIS-based map (mxd) hosted on allows the viewer to alternate between layers to understand the three-dimensional characteristics of the regions.

The ArcGIS-based map is zoomable and layers may be turned on and off to view the various geologic layers. General instructions/helpful hints for navigating on maps hosted by are as follows:

  • When you first open this project you will notice in the left hand corner “Contents” and the name “ParkCounty AquiferComb 15 06 30 online”, click on this heading.
  • Next you will notice many different categories in which you can also click on to see further data under those headings.
  • Each group or layer can be turned off and on by checking or unchecking the box next to it. Click on the name of the layer to expand the sub-layers, as needed.
  • The Group is hierarchical with the header being the highest point and can turn on everything underneath if everything is checked in that group.
  • One can zoom in or out using the + and – sign in the top left hand corner of the Geography box or by using a scrollable mouse wheel.
  • Clicking the House button will take you back to the initial start state of the map, which is the boundary of Park County.
  • Well files have a Total Depth (TD) and Water Level (WL) in feet. The “nl” labels mean that the depth or water level were “Not listed” in the DWR database.

Disclaimer: These data are intended for use at 1:50,000 scale and are checked for accuracy accordingly. The CGS does not assume responsibility for the use of these data.