In recent years, the festival has not been held due to previous disturbances. However, at around the same time inofficial horse races are being held near other Kham towns. You will have to ask around and then just go with the rumours. Western tourists are reasonably well received at these events.
This is not Yunnan, so things are just a little harder.
Next event: 01 August 2012 in Litang, Sichuan
