Kyrstin Gemar, 22, of Grossmont, Calif; Afton Williamson, 20, of Lake Elsinore, Calif.; and Ashley Neufeld, 21, of Brandon, Manitoba in Canada were believed to be in a white 1997 Jeep Cherokee with California plates when they were last heard from late Sunday night, authorities said.
Dickinson Police Lt. Dave Wallace said a friend of the women received two telephone calls from them, about one minute apart, before the line cut out. The exact words used in the calls and exactly which of the women they came from were not immediately released.
"Some place in that conversation, water was mentioned. What that context is, is speculation," Wallace said Monday night.
The friend who received the calls then called 911 to report that the women needed help.
Authorities used three airplanes and officers on the ground Monday to search within in a 30-mile radius of the cell phone tower north of Dickinson where the call came through. The search included Lake Patterson near Dickinson, which is about 98 miles west of Bismarck and 63 miles east of the Montana state line.
The air search was called off after dark with plans to resume Tuesday.
"Investigators are in the field as we speak, continuing to do interviews with friends, family and associates," Wallace said. "Nothing has been confirmed at this point, where we can say, 'Yes, they were here at this point."'
Kyrstin Gemar's father, Lenny Gemar, told ABC's "Good Morning America" in a telephone interview on Tuesday that the girls often went star gazing in the Dickinson area, and that police do not suspect foul play in the disappearance.
Wallace said relatives of the three women were expected in Dickinson by Tuesday.
Wallace refused to speculate on what might have happened and said nothing was being ruled out.
"Right now, we just have three missing young ladies," he said.