The women reported finding the bagged head of a male next to a trail in Bronson Canyon near the Hollywood sign about 2:30 p.m.
The women were walking nine dogs along a trail when two of the dogs began playing with the plastic bag and an object inside it.
"While the dogs were playing with it, at some point the object came out of the bag and they discovered it was a head. A severed head," said Los Angeles police Sgt. Mitzi Fierro.
Detectives scoured the scene in search of more body parts. They ended their search when night fell, but said they would return at sunrise. Police will be guarding the scene overnight.
Police did not say what the possible age or race of the victim, but they said the crime appears to be recent.
"The head appears to be rather new. There are not a lot of signs of decomposition yet," Fierro said.
Police said there have been no reports of a missing man in the area.
Fierro said dental records can be used to identify the victim and that a sketch may be drawn.