Tresp departed from her daughter's residence in Stillwater, Oklahoma on August 31, 1998. She was planning to drive to a religious retreat at a Benedictine monastery near Pecos, New Mexico. It has been established that Tresp purchased gasoline at a station in Santa Rosa, New Mexico at approximately 3:00 p.m. that day. She was familiar with the route to the monastery.

Tresp's white four-door 1997 Honda Civic with Arkansas license plates numbered 672-AOK was discovered locked and abandoned on forestry road 63A near the Glorieta/Pecos, New Mexico area later in the day. This location is approximately 10 to 15 miles from Route 63. Tresp's car became lodged on a large rock in the road, which cracked the oil pan. Authorities believe Tresp walked away from the vehicle to locate assistance, but it is unclear where she headed. Extensive searches of the area produced no clues as to Tresp's whereabouts. She has never been heard from again. Her purse disappeared with her and has never been found, but all her other belongings were inside the car.

When Tresp's children found out she never arrived at the monastery, they all traveled to New Mexico and began searching for her. They called hospitals to see whether she had had an accident and suffered memory loss, passed out fliers, and searched the route looking for Tresp's car. They reported her missing on September 8 after their search proved unsuccessful.

Tresp was a resident of North Little Rock, Arkansas in 1998. She was a deeply religious Catholic and enjoyed traveling. Her family stated she was mentally sharp, but she got lost easily when she was driving. Her disappearance remains unsolved.