Historical Information

Anamosa Limestone is quarried out of Stone City, Iowa, which is located along the Wapsipinicon River about two miles west of Anamosa, Iowa. Opportunities for usage of this limestone were recognized well over 100 years ago by the early settlers in the 1840’s.

During the next several decades, most major construction in the region utilized Stone City “dimension stone”. The western expansion of the railroad system facilitated distribution to bordering states and utilization of Anamosa Limestone as the primary building material for railroad bridges, bridge piers, foundations and major buildings.

In the years 1859 to 1895, over 150,000 railroad car shipments of stone originated from the Stone City area. Usage diminished rapidly with the local introduction of Portland Cement concrete in 1905, but quarry operations at Stone City survived this momentary slow-down and it remains a significant part of the Eastern Iowa economy.

For additional historical photographs, below are a few interesting websites:

Calvin's Scrapbook

Stone Quarries and Beyond

Above is a photograph taken in the early 1910's of the Anamosa State Penitentiary located in Anamosa, Iowa.  The prison was constructed by inmates with Anamosa Limestone being used as the main building material.  Click here for additional photographs.

 

Geological Information

Anamosa Limestone, a Dolomitic limestone, is a prominently laminated magnesium limestone that was deposited regionally approximately 420 million years ago across the Midwest in the Silurian interval of geological time. Numerous independent lines of evidence confirm that, at that time, Iowa lay in the tropics south of the equator.

This distinctive stone forms part of the Gower Formation, the youngest Silurian strata in Iowa. It represents the accumulation of lime extracted from seawater by animals and plants for support of their soft body tissues. Soon after deposition, the calcareous limestone was altered by infiltration of magnesium from the seawater to form dolomite. Crinkly laminations reflect the geometry of thin algal mats on the sea bottom, and planar laminations likely formed in response to seasonal or periodic changes in water chemistry. Alternations of lime mud and sand document the history of calm water interrupted by periodic storms.

The rarity of most fossil groups reflects the biologically hostile marine environment. Identical laminated dolomite strata are found associated with thick rock salt deposits in the Silurian of Michigan, and scattered evidence of the former presence of gypsum salts is also noted at Stone City. In shallower water areas adjacent to the sites of Anamosa Limestone deposition, corals, brachiopods and other marine invertebrates built spectacular contemporaneous reefal mounds that are now prime sources of concrete aggregate at other Iowa quarries. Storm erosion of these mounds provided the source of interbedded lime sands locally seen within Anamosa beds, although very few fossils are present in the Anamosa Limestone quarried at Stone City.