Search warrants were available if you had the necessary information. I was taught, though to intimidate people into letting me search their car without probable cause.
I was told to ask people to open the trunk, if I wanted to look there, and if they would not, to get a lug wrench out of the truck and tell them that the trunk was coming open, one way or another. I was told that this tactic worked every time.
I do not think people could get away with that sort of intimidation today, with ubiquitous video cameras.
I was also told that a warden could go on private land anytime he thought there was a reason to investigate possible game or fish violations on that land. I was lead to believe that there was always some way to justify going on private property if one wanted to.
Interestingly, the warden force in Wisconsin had the habit of running around on old logging roads and back trails with their lights off, attempting to catch poachers. They (unsurprisingly) had the highest accident rate of any group in the state. They were worried about liability, so they came up with a time honored solution: they lobbied the legislature and had them pass a law which granted them immunity if they had an accident while running around with their lights off.
Reminds me of a story I heard in West by God.
A warden had a dismissive attitude towards people. One day he passes a land owner without even waving so the land owner followed after him until the road narrowed and cut down a tree over the road. The warden waved after that.