Transportation to Zao Onsen and Okama

Hi

What is the last bus from Yamagata to Zao Onsen? Is there any bus operating during weekend?

And how do I access to Okama from Zao onsen?
I see there is only one bus daily to Yamagata, how do I return to city from there?

Thank you!

What is the last bus from Yamagata to Zao Onsen?

It departs Yamagata Station at 18:55:
http://www.yamakobus.co.jp/rosenbus/jikoku/frame/zao-onsen.html

Is there any bus operating during weekend?

Yes.

And how do I access to Okama from Zao onsen?
I see there is only one bus daily to Yamagata, how do I return to city from there?

On weekends only (outside of winter) there is one bus that continues to Okama. It leaves Zao at 10:10 and arrives at the summit at 11:06. Then departs again in direction of Zao and Yamagata at 13:00.