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Green Mountain, Golden, Golden District, Jefferson Co., Colorado, USA

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Latitude & Longitude (WGS84): 39° 42' 54'' North , 105° 10' 19'' West
Latitude & Longitude (decimal): 39.71500,-105.17194
GeoHash:G#: 9xj1yvbhs
Locality type:Mountain
Köppen climate type:Dfb : Warm-summer humid continental climate

Green Mountain is located approximately 4 miles south of Golden and stands approximately 800 feet above the surrounding country. From a distance it appears somewhat elliptical in profile; steep sided and a broad, much more gently rounded top. Close up the mountain slopes are in fact steep but are quite irregular being cut by many ravines. Years ago some of the ravines and the ridges between them were the site of jeep trails. This author remembers the top 50 feet of one of those trails as the steepest, scariest pitch he ever navigated with a motor vehicle.

The lower part of Green Mountain is underlain by the sands, shales and claystones of the lower Paleocene Denver Formation. The upper part is composed largely of Paleocene age Green Mountain conglomerate deposited just east of the Golden fault which marks the abrupt eastern edge of the Rocky Mountains. The Green Mountain formation conglomerate contains a substantial amount of silicified wood.

On the northeastern, lower slopes of Green Mountain is a small, now destroyed or buried outcrop of the 3rd Table Mountain lava flow, Tv3 (Drewes, 2008). This is the zeolite producing flow at nearby North Table Mountain and accounts for the zeolites listed from this locality. The given coordinates are approximate for the lava outcrop.

In the late 1960's and early 1970's suburban sprawl sprawled right up to the eastern and northern edges of Green Mountain. Fortunately the mountain itself has been made a 2400 acre open space park.

Select Mineral List Type

Standard Detailed Strunz Dana Chemical Elements

Mineral List

5 valid minerals.

Detailed Mineral List:

Formula: CaCO3
Reference: Minerals of Colorado (1997) E.B. Eckel
'Heulandite subgroup'
Reference: Minerals of Colorado (1997) E.B. Eckel
Formula: (Na2,Ca,K2)4(Al8Si40)O96 · 28H2O
Reference: Minerals of Colorado (1997) E.B. Eckel
Formula: SiO2 · nH2O
Reference: Minerals of Colorado (1997) E.B. Eckel
Opal var: Fire Opal
Formula: SiO2 · nH2O
Reference: Minerals of Colorado (1997) E.B. Eckel
Opal var: Wood Opal
Formula: SiO2 · nH2O
Reference: Minerals of Colorado (1997) E.B. Eckel
'Petrified Wood'
Description: Also palm wood
Reference: Minerals of Colorado (1997) E.B. Eckel
Formula: FeS2
Reference: Minerals of Colorado (1997) E.B. Eckel
Formula: SiO2
Reference: Minerals of Colorado (1997) E.B. Eckels
Quartz var: Agate
Reference: Minerals of Colorado (1997) E.B. Eckel
Quartz var: Chalcedony
Formula: SiO2
Reference: Minerals of Colorado (1997) E.B. Eckel

List of minerals arranged by Strunz 10th Edition classification

Group 2 - Sulphides and Sulfosalts
Group 4 - Oxides and Hydroxides
Opal4.DA.10SiO2 · nH2O
var: Fire Opal4.DA.10SiO2 · nH2O
var: Wood Opal4.DA.10SiO2 · nH2O
var: Agate4.DA.05SiO2
var: Chalcedony4.DA.05SiO2
Group 5 - Nitrates and Carbonates
Group 9 - Silicates
Mordenite9.GD.35(Na2,Ca,K2)4(Al8Si40)O96 · 28H2O
Unclassified Minerals, Rocks, etc.
Heulandite subgroup-
Petrified Wood-

List of minerals arranged by Dana 8th Edition classification

Group 2 - SULFIDES
AmBnXp, with (m+n):p = 1:2
Group 75 - TECTOSILICATES Si Tetrahedral Frameworks
Si Tetrahedral Frameworks - SiO2 with [4] coordinated Si
Si Tetrahedral Frameworks - SiO2 with H2O and organics
Opal75.2.1.1SiO2 · nH2O
Group 77 - TECTOSILICATES Zeolites
Zeolite group - True zeolites
Mordenite77.1.6.1(Na2,Ca,K2)4(Al8Si40)O96 · 28H2O
Unclassified Minerals, Rocks, etc.
'Heulandite subgroup'-
var: Fire Opal
-SiO2 · nH2O
var: Wood Opal-SiO2 · nH2O
'Petrified Wood'-
var: Agate
var: Chalcedony-SiO2

List of minerals for each chemical element

H Opal (var: Fire Opal)SiO2 · nH2O
H Mordenite(Na2,Ca,K2)4(Al8Si40)O96 · 28H2O
H OpalSiO2 · nH2O
H Opal (var: Wood Opal)SiO2 · nH2O
C CalciteCaCO3
O CalciteCaCO3
O Quartz (var: Chalcedony)SiO2
O Opal (var: Fire Opal)SiO2 · nH2O
O Mordenite(Na2,Ca,K2)4(Al8Si40)O96 · 28H2O
O OpalSiO2 · nH2O
O QuartzSiO2
O Opal (var: Wood Opal)SiO2 · nH2O
Na Mordenite(Na2,Ca,K2)4(Al8Si40)O96 · 28H2O
Al Mordenite(Na2,Ca,K2)4(Al8Si40)O96 · 28H2O
Si Quartz (var: Chalcedony)SiO2
Si Opal (var: Fire Opal)SiO2 · nH2O
Si Mordenite(Na2,Ca,K2)4(Al8Si40)O96 · 28H2O
Si OpalSiO2 · nH2O
Si QuartzSiO2
Si Opal (var: Wood Opal)SiO2 · nH2O
S PyriteFeS2
K Mordenite(Na2,Ca,K2)4(Al8Si40)O96 · 28H2O
Ca CalciteCaCO3
Ca Mordenite(Na2,Ca,K2)4(Al8Si40)O96 · 28H2O
Fe PyriteFeS2

Regional Geology

This geological map and associated information on rock units at or nearby to the coordinates given for this locality is based on relatively small scale geological maps provided by various national Geological Surveys. This does not necessarily represent the complete geology at this locality but it gives a background for the region in which it is found.

Click on geological units on the map for more information. Click here to view full-screen map on

0.0117 - 2.588 Ma

ID: 2443468
Slocum Alluvium

Age: Pleistocene (0.0117 - 2.588 Ma)

Description: Bouldery cobble gravel near mountain front, decreases in grain size eastward away from mountains. Much calcium carbonate (CaCO3) in upper part where not removed by erosion. Many unsound stones. Thickness generally less than 7.6 m. Forms gently sloping surfaces 24 to 36 m above present streams.

Reference: Trimble, D.E., M.N. Machette. Geologic Map of the Greater Denver Area, Front Range Urban Corridor, Colorado. U.S. Geological Survey Geologic Investigations Series I-856-H. [64]

Early Pleistocene - Pliocene
1.806 - 5.333 Ma

ID: 2208230
Rocky Flats Alluvium

Age: Cenozoic (1.806 - 5.333 Ma)

Description: Mostly quartzite-rich cobble and pebble gravel that contains beds and lenses of pebbly sand, silty sand, and pebbly sandy clay at its type area on Rocky Flats about 9 km south of Boulder; mostly gravelly alluvium interbedded with pebbly silt and clay elsewhere in piedmont portion of map area. Some of the silty and clayey sediment mantling or within upper part of unit may be of eolian origin (Reheis, 1980; Shroba and Carrara, 1996). At Rocky Flats, upper part (typically ≤5 m) of unit forms an alluvial fan that locally buries a hogback composed of Fox Hills Sandstone (Kf), and lower part of unit (≤25 m) fills small basins and paleovalleys that are cut in Cretaceous sedimentary rocks. Paleovalleys radiate eastward away from apex of fan (Knepper, 2005; Lindsey and others, 2005). Elsewhere in map area, unit forms pediment and valley-fill deposits. At its type section (Scott, 1960), the soil formed in upper part of unit has an A/Bt/K profile with stage III–IV carbonate morphology. This soil directly overlies a buried soil that has a Btk/K/Btk profile with stage I and stage III carbonate morphology. Amount of cobbles and boulders in unit decreases with increasing distance east of mountain front. Unit consists of fan deposits and valley-fill deposits that mantle a dissected landscape at Rocky Flats (Knepper, 2005); elsewhere in map area consists of relatively thin pediment and valley-fill deposits. Soil properties and paleomagnetic data suggest that the Rocky Flats Alluvium is at least 1.6–1.4 Ma (Birkeland and others, 1996) and could be about 2 Ma (Birkeland and others, 2003). Cosmogenic dating (on 10Be) indicates that upper part of the Rocky Flats Alluvium at Rocky Flats is about 1.5 Ma (Dethier and others, 2001); buried soils formed in upper part of unit suggest that the underlying valley-fill deposits in lower part of unit could be much older. Recent cosmogenic dating (on 10Be and 26Al) suggests that incision of eastern part of Rocky Flats surface began about 2–1 Ma (Riihimaki and others, 2006). A small area of Rocky Flats surface, which extends northeastward from the mouth of Coal Creek Canyon (red circle pattern), displays a braided pattern produced by subdued gravel bars and shallow channels. These features may have been produced by a major flash flood on Coal Creek that flowed across the Rocky Flats surface. Age of flash flood is inferred to predate the Verdos Alluvium (Qv), which is inset below Rocky Flats surface along Coal Creek. Top of Rocky Flats surface is about 140–230 m above most major streams near mountain front. Unit QNr is a source of coarse aggregate. Thickness at Rocky Flats commonly less than 6 m but locally greater than 40 m (Knepper, 2005); elsewhere in map area commonly about 3–6 m thick

Reference: Kellogg, K.S., Shroba, R.R., Bryant, Bruce, and Premo, W.R. Geologic Map of the Denver West 30' x 60' Quadrangle, North- Central Colorado. USGS Geologic Investigations Series 3000. [35]

Paleocene - Late Cretaceous
56 - 100.5 Ma

ID: 2954406
Denver and Arapahoe Fms

Age: Phanerozoic (56 - 100.5 Ma)

Stratigraphic Name: Denver Formation; Arapahoe Formation

Description: Sandstone, mudstone, claystone, and conglomerate; Denver is characterized by andesitic materials

Comments: Original map source: Green, G.N., 1992, The Digital Geologic Map of Colorado in ARC/INFO Format: U.S. Geological Survey Open-File Report 92-0507, 9 p., scale 1:500,000.

Lithology: Major:{sandstone,mudstone,conglomerate}, Minor:{claystone,andesite}

Reference: Horton, J.D., C.A. San Juan, and D.B. Stoeser. The State Geologic Map Compilation (SGMC) geodatabase of the conterminous United States. doi: 10.3133/ds1052. U.S. Geological Survey Data Series 1052. [133]

201.3 - 251.902 Ma

ID: 3191821
Mesozoic sedimentary rocks

Age: Triassic (201.3 - 251.902 Ma)

Lithology: Sedimentary rocks

Reference: Chorlton, L.B. Generalized geology of the world: bedrock domains and major faults in GIS format: a small-scale world geology map with an extended geological attribute database. doi: 10.4095/223767. Geological Survey of Canada, Open File 5529. [154]

Data and map coding provided by, used under Creative Commons Attribution 4.0 License


Sort by

Year (asc) Year (desc) Author (A-Z) Author (Z-A)
Eckels, E.B. (1997), Minerals of Colorado.
Drewes, Harald (2008), Table Mountain shoshonite porphyry lava flows
and their vents, Golden, Colorado: U.S. Geological Survey Scientific
Investigations Report 2006–5242, 28 p.

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