Is the park open during the winter? I am a trainer/coach at a local gym and we are looking for a good place to do some outside training for the upcoming spartan race at Greek Peak in March 2019. So, we would be looking to go trail running Nov- Feb

Yes

It's open in the winter time. I go there to clear my head when there's 2 feet of snow on the ground. Then I regret it later because my feet get soaked. But yeah clarks is open all year. Most state parks are.

As far as I am aware it is open all year but you only have to pay to get in between Memorial Day and Labor Day.

The park is only open Dawn to Dusk. The absolute hours listed by Google are incorrect.