A social services employee visited Jaime Sheridan's Castle Valley home Friday afternoon, which may have scared the mother into thinking the state may be trying to take custody of the boy, Nyland said.
Sheridan's father last saw his daughter and grandson about 10 p.m., according to the sheriff's office. The father awoke about 5:30 a.m. Saturday after noticing the home was cold.
Sheridan's father found an open door, but not Sheridan, who suffers from a mental illness, or her son.
"We found tracks towards the road from the residence," the sheriff said.
Authorities don't know whether Sheridan and the boy caught a ride from a passing motorist or if they went walking into the night in single-digit temperatures. Sheridan doesn't own a vehicle and left her driver's license behind.
A door-to-door search throughout the Castle Valley wasn't fruitful. A county search and rescue crew was expected to being looking for the pair Saturday afternoon.
After a possible sighting of the mother at a Moab motel, about 10 miles west, a deputy was dispatched with a photo, but Nyland was unaware whether the sighting was Sheridan.
Sheridan is described as 5 foot 2 inches tall, 85 to 100 pounds, with long brown hair to the middle of her back. She was last seen wearing red sweat pants and an Army fatigue jacket.
Her 5-year-old son is described as having wavy brown hair in a ponytail. He was last seen wearing a white furry sleeper, diaper and black gloves.
Anyone with information is asked to call the Grand County Sheriff's Office at 435-259-8115.