Statement of Significance (as of designation - May 16, 2000):
The Portland Brownstone Quarries were the main source of the distinctive reddish-brown sandstone called "Brownstone," which was used so extensively in building construction during the latter half of the 19th century that this period has become known as the "Brownstone Era." Used for mansions and middle class houses alike, brownstones embodied the prosperous, progressive image of America during that period of national expansion and economic growth. The quarries also are importantly associated with American geologist Paul Dimitri Krynine, who used data collected from the site in a definitive study to determine the geological origin of "redbeds." While "redbeds" were once thought to indicate only arid, desert-like environments, Krynine, relying on features in the Portland quarries, demonstrated in what is now a classic geological work on their origin that they also formed under warm, humid, tropical conditions.