The stabbing was reported just before 6 a.m. on an embankment near northbound Highway 41 and Shaw Avenue, officers say.
Authorities said a man and a woman at an illegal encampment were involved in a fight when a 55-year-old man approached and attempted to break them up.
Investigators say the victim was then stabbed by the man involved in the argument.
The victim was taken to a hospital for treatment. His condition is unknown.
CHP has not released a description of the suspect as the investigation continues.