Boulder park warns that all bags "subject to search"

Search-In-Boulder


When I was in Boulder, CO last week I went for a walk in a city-owned "greenbelt" hiking trail. I saw this sign that read, "All bags and coolers subject to search. City of Boulder Rangers and Police Officers will be patrolling this area."

Are the police allowed to search your bags in a public park without a warrant? (I saw no police officers or rangers while hiking that day; in fact I saw no other hikers either.)