Investigators said they are unsure if the remains are those of a man or a woman.
They said the medical examiner's office will conduct an autopsy on the possible remains.
Deputies said Montalvo was last seen at about 5 p.m. Monday dropping off her son at Hixon Avenue. She was reported missing Thursday.
Investigators said Montalvo was supposed to pick up her son from Harmony School on Tuesday but she never did so.
Investigators had searched the property -- including a construction shed, recreational vehicle and trailers -- for Montalvo or evidence relating to her disappearance.
"There's a wooded area and a pond in that property, and so we are going to comb the entire property," Ruiz said.
"It's not like her to drop off her son and not pick him back up," she said. "He's her world, so that's all she did -- be with him, spend time with him."
Records said Montalvo called deputies last year to report that her estranged husband and another person took her to a secluded area, where he slapped her across the face several times because he didn't like her texting a friend and taking his son.
The documents said he threw her to the ground and attempted to break her neck, saying she would be killed if she called 911.
Earlier this month, Montalvo sent a handwritten letter to a judge asking that a protection order she had against her husband be dropped because it would be best for her son.
Montalvo was last seen wearing a gray shirt and blue jeans.
Investigators said her phone has been off for several days.