PHOTOS: Historic inscriptions at Aztec Ruins National Monument | Sept. 19

Colorado historian, author and researcher Fred Blackburn stands outside the West Ruin at Aztec Ruins National Monument, where he is conducting an extensive survey of the park's historic inscriptions.

The signature of Boyd Abrams, one of the members of a family that once owned the Aztec Ruins site, is visible on a latilla in the West Ruin of the park.

Archaeologist Victoria Atkins, left, and intern Moriah Sonnenberg are part of the team assisting historian Fred Blackburn in his survey of historic inscriptions at Aztec Ruins National Monument.

The large signature of a W.E. Black is visible on the side of a viga in the West Room at Aztec Ruins National Monument.

Researcher Fred Blackburn stands inside one of the rooms in the West Ruin at Aztec Ruins National Monument where he is conducting a survey of historic inscriptions.

The 1908 signature of Kansas resident P.P. Eizen is found on the side of a viga in the West Ruin at Aztec Ruins National Monument.

Some of the vigas in at Aztec Ruins National Monument are marred by holes or plugs left when core samples were taken from them to determine their age, Fred Blackburn says, explaining that such practices used to common archaeological procedure.