The following is reprinted from an excellent website RevolutionaryWarNewJersey.com

The obelisks were erected by the New Jersey Sons of the Revolution in March 1914. The actual construction and installation of the obelisks was done by the John L. & William Passmore Meeker company of Newark. The obelisks were most likely placed at their twelve locations sometime in April or May 1914. [28]  The Meeker company ran a steam-powered workshop on Market Street in Newark that made marble and granite monuments. They opened in 1860 [29] and were successful and noted enough to have received a commission from the state of New Jersey to create monuments to New Jersey troops at Maryland's Antietam Battlefield National Park in 1902 - 1903.

A March 8, 1914 article in the Trenton  newspaper the Sunday Times-Advertiser reported that these obelisks were about to be built. The article described in great detail the construction of the obelisks, making a great point of how sturdily they were to be constructed:

"The obelisks are to be made of the best Quincy granite and will be rock faced on all four sides. They will be eight feet tall, but two feet of this length will be set in the ground, imbedded in concrete, to make their removal all but impossible. They will be one foot six inches on each side. Bronze tablets, one foot wide by sixteen inches tall, will be set in the front face of each obelisk at little above the middle of the length. They will be recessed in the rock and fastened with the greatest firmness and by means of bolts that will be invisible from the surface of the tablets. The bolts will, morever [sic], be located at points in the tablet that would scarcely be suspected."

Click here for the Google map to the twelve obelisks