Stayner didn't speak during his arraignment in federal court in Fresno, California. His federal defender, Robert Rainwater, entered a plea of not guilty on his behalf.
Law enforcement sources have said that Stayner has confessed to killing Armstrong and three other women who were sightseeing in the park earlier this year.
The three sightseers, Carole Sund, 42, her daughter, Juli, 15, and family friend Silvina Pelosso, 16, vanished on Feb. 15 from the Cedar Lodge in El Portal, on Yosemite's western doorstep.
Stayner was led into the courtroom in a bright yellow jumpsuit, his feet and hands shackled. He kept his eyes downcast and did not look at his parents, who were sitting together, holding hands in the front row.
The hearing lasted about two minutes. Stayner was ordered back into the custody of U.S. marshals.
U.S. Magistrate Sandra Snyder gave the government ten days to provide the defense with the evidence it has discovered against Stayner, and set a status conference for August 19th.
If Stayner is found guilty of slaying the naturalist, he could receive the death penalty.
Meanwhile, an imprisoned convict whom the FBI was relying on to help solve the case of the three slain sightseers said Thursday he falsely implicated himself in hopes he'd get off easy on unrelated charges.
During a prison interview with The Associated Press, Eugene "Rufus" Dykes said he told investigators so many different stories Â— some linking himself and others to the murders Â— that he couldn't think of any more.
Last month, authorities announced that the killers were likely a group of people who were already in jail for other crimes. But days later, they arrested Stayner.
FBI agent Nick Rossi would not comment on any of Dykes' claims.
Dykes said he feels badly that someone else died before FBI agents caught the alleged killer. He also said he doesn't know Stayner.