The Guilford Quartz Monzonite was described in 1898 as "perhaps the most attractive stone in the state" by Edward B. Mathews of the Maryland Geological Survey.

During the succeeding twenty-five years the operations were of little account, and little work was done until the Guilford and Waltersville Granite Company attempted to develop the industry in 1887.

The industrial life of the district has been revived somewhat in recent years by the operations of Messrs. Matthew Gault and Sons, who commenced work in 1893, and by Messrs. Brunner and White, who opened a quarry of superior quality in March, 1895.A.

A. Drake argued that the Guilford is of Ordovician age[5] because it is probably comagmatic with the Woodstock Quartz Monzonite dated at 444 Ma.

[6] More recently, radiometric dating (U-Pb-TIMS) of zircon crystals extracted from the Guilford Quartz Monzonite yielded an age of 362 +/- 3 Ma (Devonian).