Soil series profile

Sphinx soil series

Sphinx is a somewhat excessively drained soil with a gravelly coarse sandy loam surface, mapped on 185,893 acres in 5 counties in CO. Hydrologic group D.

#1969 by mapped area sandy-skeletal Typic Ustorthents (Entisols)

Drainage class: Somewhat excessively drained
Hydrologic group: D
Typical topsoil pH: 6.7
Mapped area: 186k

Typical Sphinx profile

Texture and pH by depth

Depth to scale. More strongly shaded layers hold more clay. Horizon names are the soil survey's (A = topsoil, B = subsoil, C = parent material).

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Typical Sphinx horizons (representative values)
Depth	Texture	pH	Clay	Sand	Organic matter
0–1 in (Oi)	Slightly decomposed plant material	5.6	10%	66%	85%
1–5 in (A)	Gravelly coarse sandy loam	6.7	10%	66%	1.5%
5–13 in (AC)	Very gravelly loamy coarse sand	5.8	8%	82%	1.5%
13–61 in (Cr)	Bedrock	Not reported	Not reported	Not reported	Not reported

Representative values from the most extensive Sphinx map unit (Sphinx-Rock outcrop complex, 15 to 80 percent slopes, survey area CO640). Other map units of this series vary within the series range.

Stock photo for illustration, not a sample of this soil series. Credit on the Sources & method page.

What this means

What Sphinx soil means for gardens, lawns and septic systems

For gardens

Typical topsoil in Sphinx soils is neutral: pH 6.7, the range most vegetables, flowers and lawn grasses prefer.

Loamy topsoil (loam, silt loam and similar) covers >99% of mapped Sphinx acres: generally the easiest soil to garden, holding moisture without staying waterlogged. The most common surface texture is gravelly coarse sandy loam (98% of mapped Sphinx acres).

100% of mapped Sphinx acres is excessively or somewhat excessively drained: water moves through fast, so gardens need more frequent watering in dry spells.

For lawns and yards

On >99% of mapped acres, rain soaks in slowly (hydrologic groups C and D, including dual groups that are D until drained). Expect runoff and puddles after heavy rain: core-aerate compacted lawns and keep ground sloping away from foundations.

For a septic system

For conventional septic absorption fields, NRCS rates >99% of the acres in mapped Sphinx soils very limited, 0% somewhat limited and 0% not limited.

Where the soil is very limited (slow permeability, a high water table, flooding, shallow bedrock or steep slopes), alternative systems such as mound or sand-filter designs are common and cost more.

Only a licensed site evaluation or perc test at the actual lot decides whether a system is allowed and which design.

Generated from the mapped numbers above using fixed rules, not a site visit. See how these notes are written.

Where Sphinx soil is found

Mapped acres

Sphinx is mapped in Colorado.

Counties with the most mapped Sphinx soil
County	Acres	Share of county land
Douglas County, CO	71,862	13.4%
El Paso County, CO	46,183	3.1%
Teller County, CO	44,688	12.5%
Jefferson County, CO	22,424	5.5%
Park County, CO	29	0.0%

Septic absorption fields

NRCS rating, share of Sphinx acres

Not limited 0%

Somewhat limited 0%

Very limited >99%

Not rated <1%

Septic tank absorption field rating across mapped Sphinx acres. Scale 0 to 100% of mapped land.

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Septic tank absorption field rating across mapped Sphinx acres.
Category	Share of acres
Not limited	0.0%
Somewhat limited	0.0%
Very limited	99.8%
Not rated	0.2%

Drainage, water table and flooding

Share of Sphinx acres

Depth to seasonal high water table: None reported within about 6.5 feet (median where reported).
Flooding: Not mapped as flooding on most acres.
Slope: Typically 28–55% (median 43%).
Topsoil organic matter: Median 1.5%.

Drainage class

Excessively drained 0%

Somewhat excessively drained 100%

Well drained 0%

Moderately well drained 0%

Somewhat poorly drained 0%

Poorly drained 0%

Very poorly drained 0%

Drainage class across mapped Sphinx acres. Scale 0 to 100% of mapped land.

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Drainage class across mapped Sphinx acres.
Category	Share of acres
Excessively drained	0.0%
Somewhat excessively drained	100.0%
Well drained	0.0%
Moderately well drained	0.0%
Somewhat poorly drained	0.0%
Poorly drained	0.0%
Very poorly drained	0.0%

Hydrologic soil group

A: fast infiltration (mostly sandy or gravelly) 0%

B: moderate infiltration 0%

C: slow infiltration 0%

D: very slow infiltration (clayey, shallow or wet) >99%

A/D: D as is, A if drained 0%

B/D: D as is, B if drained 0%

C/D: D as is, C if drained 0%

Not rated <1%

Hydrologic soil group across mapped Sphinx acres. Scale 0 to 100% of mapped land.

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Hydrologic soil group across mapped Sphinx acres.
Category	Share of acres
A: fast infiltration (mostly sandy or gravelly)	0.0%
B: moderate infiltration	0.0%
C: slow infiltration	0.0%
D: very slow infiltration (clayey, shallow or wet)	99.8%
A/D: D as is, A if drained	0.0%
B/D: D as is, B if drained	0.0%
C/D: D as is, C if drained	0.0%
Not rated	0.2%

Sources & data dates

Source: USDA NRCS Soil Survey Geographic Database (SSURGO), queried through Soil Data Access. Public domain.
Data date: SSURGO as published on November 3, 2026 (most recent survey area update October 26, 2026). NRCS refreshes SSURGO each October.
Scope: All map unit components named Sphinx (component kind "Series") in SSURGO: 185,893 acres.
Method: Shares are by mapped acres of Sphinx components. The profile comes from the single largest Sphinx component. Full methodology.

Independent reference site. No government affiliation or endorsement.

Full narrative description: USDA Official Soil Series Description for Sphinx.