Drake Kramer, 21, of San Antonio, was last seen Sunday morning checking out of the Bright Angel Lodge, officials said.
His father, Robbin Kramer, said his son told him Monday that "he was at the Grand Canyon and he needed to be back with Mother Earth and set his soul free. At that point we really started getting worried and started calling and trying to get people to look for him."
The family reported Drake Kramer missing on Monday, and search efforts and a missing person investigation are now under way.
"He posted on his Facebook when he was out here with his aunt last time: 'Wish I could stay.' And he had other posts about ... places he'd like to see, like the Redwood Forest, before he dies," Robbin Kramer said.
"We're focusing on the positive by trying to believe that him saying he needed to be with Mother Earth and set his soul free that he was talking about being out in nature and being one with nature," he said.
Drake Kramer loves to be outdoors and camp, his father said, but he's not sure if his son took appropriate hiking equipment with him.
"He was on the road to be a geologist so he could be out in nature where he loves to be," Robbin Kramer said.
Drake Kramer drove out west on I-10, according to his father.
"There had to be people that saw him when he filled up for gas. We'd really like to know if anyone saw him purchase any of the appropriate equipment with cash," Robbin Kramer said. "If anyone along the way saw him, heard anything, any information would be great."
Kirby-Lynn Shedlowski with the Grand Canyon National Park told ABC News, "We don't know what his plans were. He may be hiking, we just don't know."
"Nobody is sure where he is, what he's doing, if he's OK," Robbin Kramer said. "So many people that love him and are worried about him. Everyone is just on the edge of their seat."
Drake Kramer is described as having brown hair and blue eyes. He is 5 feet 7 inches tall and 140 pounds, officials say. Anyone with information can call the National Park Service Silent Witness Line at 928-638-7840.