Does the park close at some point?

I believe it closes at sunset

Sunset for sure

Only the area adjacent to the lake closes at sunset. The camping areas and trails and streams are always open.

The park is open year round: 8 A.M. to sunset April to October and 10 A.M. to sunset November to March. However, the man-made lake is drained during the winter.

I never saw any posted hours, in lieu of that, i'd go with the sunset possibility as well.