(CNN) -

They had plans for the holiday weekend, to visit the zoo and stop by an amusement park. But now Lore Heavilin just wants her daughter to come home.

Nineteen-year-old Erin Corwin vanished without a trace more than a week ago. Corwin, the pregnant wife of a Marine, went missing in Southern California on June 28 while scoping out photography locations at Joshua Tree National Park.

Her husband, Jonathan Wayne Corwin, reported her missing the following day.

Since her disappearance, search teams have combed through the area on foot and have searched by air, but they have not been able to track Corwin's whereabouts. The police say her disappearance is suspicious, and homicide investigators are taking the lead in the case now.

Earlier this week, police found Corwin's car in Twentynine Palms, near the military base where her husband is stationed. He has not been charged and no other leads have surfaced in the case.

Days after Corwin's disappearance, her mother learned she was going to be a grandmother. "It just doesn't seem real," she said. "Her ringtone on my phone is a horse neighing and galloping, and I would give anything to hear that ringtone. Anything."