The fires erupted one after another starting shortly after midnight along railroad tracks owned by Pan Am Railways, said Fire Investigator Paul Ouellette.
The first fire was reported near Main Street behind Salvation Army, he said. Once the first fire was knocked down, a second blaze was reported off of Libby Avenue, which damaged machinery and utility trailers owned by a local contractor, Ouellette said.
Railroad crews arrived after the fires were extinguished to move the ties and hose down smoldering embers.
Investigators hadn't identified any suspects as of 10 a.m. Monday.