The scheme is an initiative by the Howardian Hills Area of Natural Beauty (AONB) project which covers some 80 square miles of the district, including many beauty spot villages.
The manager, Paul Jackson, said the Monument Management Scheme set up by the Helmsley-based AONB (funded by Historic England and aided by the North York Moors National Park Authority) is tackling a total of 27 historic landmarks.
An initial round of surveys have been carried out, said Mr Jackson, followed by detailed reports.
He said: “Bracken control work is on-going on 23 scheduled monuments and brambles and scrub have been cleared from 27 monuments.
“In total, management work has begun on 38 monuments and the improvements are already starting in their conditions.”
Mr Jackson said that at the end of the four year project a follow-up survey will be carried out by the volunteers to assess the full beneficial impact of the work.
The value of the volunteers’ work on the monuments has been estimated at around £19,000.