Can a Park Ranger Search Me?

yes

But they did see something wrong. Just because you do not feel you are suspicious if the officer (rangers are peace officers in your state) can elucidate the reason(s) they felt you were suspicious enough the bag search or even most pat downs ares legal and any evidence found is good in court or for an arrest. Once arrested a full search is warranted.

You and your friends do not have the training nor experience to decide if you yourself are suspicious or in your own case already breaking the law.by remaining in the park after close.

" We were doing nothing wrong but some of us had Alcohol in our bags the park rangers searched us ..."

He can't search without consent for no reason. If he saw alcohol he could search, especially if it is prohibited in the park. He could ask to search for any reason. If you say "yes" he has the right.

if you are in their park they have every right to search you if they had probable cause. were you guys acting rowdy? or shady?

Apparently so.