Xian Tourist Line to Zhashui Karst Cave still in operation?

Yes, the bus is still in operation, and it can take you directly to the entrance. It departs at 7:30, 8:30, 9:00, 9:30, 10:00, 10:30, 11:30, 12:30, 13:00, 14:00, 15:00, 15:30, 16:00, 17:00, 17:30, and 18:30 from Xian Bus Station in 354 Jiefang Rd, Xincheng District.
As for returning bus, I only know it’s also a regular bus, you may reach the station for detailed information.

Hi Max, thank you for the reply! Do you happen to know the bus number too?
Are you working in Xi'an or have just been there?

I’ve visited the city last year, and I happen to get the bus schedule. But the bus number doesn’t matter, since it’s the regular bus and you just need to choose at which time you would like to take it.

Hi Max, thanks again for the answer. How about the timing for returning buses back to Xi'An? Are they on regular 30 minutes interval too?

As well, how's your visit to the caves? How many cave are we actually allow to visit? I think there's 3 to 4 caves open now? Do we need a guide to enter the cave? The website does not seems to provide much information.