Is a visa necessary to visit

Im getting conflicting information. Im an American (US passport) working in Northeast China. Do I need to get a visa prior to making a land crossing from China or will I just get my passport stamped when I cross the border to Mongolia.

Already have a multi-entry Chinese visa, but my max stay of 90 days is approaching.

No visa for Mongolia needed for US passport holders for short stays <30 days. See this for description of procedure, as described by Beijing-based border runners using the Erlian crossing:

http://www.thebeijinger.com/forum/2008/04/06/How-to-get-your-visa-exit-stamp-in-Mongolia

No visa is required for US citizens if staying for 3 month or less. This is a fairly new regulation according to the Washington DC Mongolian Embassy website

What about people from Australia?
Do they needs a Visa to enter Mongolia for less than 30 days?

cruiseman - Australians and almost everyone else except Americans and Israelis need a Mongolian visa.

It can be obtained in Beijing or Erlian (the border town) but increasingly reports suggest that if obtained in China you will need a letter of invitation or something from a travel agency or guest house confirming your plans.

OP - there is a relatively recent report of someone in your situation who described crossing from China, getting his passport stamped for exit and then crossing into Mongolia getting the entry and exit stamp and crossing back to China on the same day. You might try searching for it as this person included all information about costs and times if I recall correctly.

Also this post from summer 2007 by manulike with update from Nov 2008 has useful information: Erlian Fact Sheet.

Ruth

cruiseman - Yes you need a visa for a stay of less than 30 days, but visa rules for Australians changed recently. You used to be able to get a visa on arrival (assuming you arrived by plane into UB), but now the rules say you have to get your visa before arriving (from the embassy in Canberra - they moved from the office in Sydney recently as well). You can still get a visa in China as well if you can't get it in Australia before you leave. But you can't get them on arrival anymore. I just sent off my paperwork to Canberra for a new 12 month visa.