There are five
geological requirements for a hot spring.
Springs is a dominant discharge area for the headwaters of the San
Flowing from the west, north, and east, streams
and creeks feed into the San Juan River and recharge the
There are two major rock formations in the Pagosa
Springs area: Mancos Shale, which is the more recent, and lying
beneath that the Dakota Sandstone.
The Dakota Sandstone has been
lifted up and tilted, actually being exposed to the surface west and
southwest of Pagosa Springs.
Water movement within the tilted
strata flows down-gradient to Pagosa Springs and recharges the
Being highly porous, the sandstone acts like a sponge
and becomes an area of subsurface water
The aquifer that feeds the Pagosa Hot
Springs lies in the Mancos Shale and Dakota Sandstone formations.
The Dakota Sandstone yields the hottest subsurface
temperatures, averaging 160 degrees.
The hot water finds its way
to the surface through extensive interconnecting vertical
A layer of impermeable strata forms a
natural lid that seals in heat and prevents evaporation.
rock for the Pagosa Hot Springs is the Mancos Shale.
On a world-wide scale, temperatures rise with increased
depth as the earth releases its internal heat. Localized
increases of subsurface termeratures are associated with magma
chambers that exist in volcanic fields. These fields can be
either active or dormant as it takes hundreds of thousands of years
for this deep-seated magma to cool.
Faulting, which is associated
with tectonic activity, can be a heat source also, due to the
compressional or tensional forces that occur.
Locally, the heat
source has not been definitely defined. It will take
additional research of the area to do so.
layers of sedimentary strata that lie between the heat source and
the aquifer act as a heat conductor.
Pagosa Springs is located
within the San Juan Basin and is bound to the north and east by the
San Juan Mountains, which are sedimentary and volcanic in
During the Jurassic and Cretaceous periods much of the
western United States was covered by a shallow inland sea. The
rise and fall of the sea deposited sediments of alternating clay,
sand, silt, and gravel. The sediments were compacted and
cemented to form the rock strata of the area.
deposition of marine sediments, volcanic activity deposited 15
layers of lava and ash over the San Juan Mountains for 20 million
Crustal movement has caused folding and faulting of the
Earths crust. Pagosa Springs lies on the eastern edge of the
Archuleta Arch, which is a regional tectonic fold. The uplift
of the Arch has caused sedimentary strata to break and slip,
creating faults and tilting the strata with a dip to the NNE.
smaller folds, the Sunetha and Stinking Springs Anticlines, locally
altered the regional dip. Smaller faults associated with the Nacimiento Fault are a
source of migration for the hot mineral water from the aquifer to the