- Post from Lee
Unusual Soda Dam in the Jemez Mountains
Just north of the Jemez Springs village is a natural soda dam, one that has formed over millions of years from minerals found in the hot springs of the Jemez River. Calcium Carbonate, one of the most prominent minerals of the formation, has been deposited in a rounded formation that created small caves. The Jemez River runs at the southern boundary of the Valles Caldera where deep magma deposits heat water that flows through Pennsylvanian limestone and shale. At one time, the dam waters flowed over the top of the dam we see today, but due to diversions and blasting for road paving in 1960, the river now passes through the dam in a small waterfall.
Across the road to the west, Precambrian gneiss can be seen in the road cut. This ancient rock is mostly impermeable, which forces hot spring water through the limestone layers along a small fault. Green and purple layers seen near the waterfall are collections of bacteria.