Im coming from USA to hike Mt. Huashan. Im wondering where I fly into and what route from there.

You may fly into Xian. Upon landing, take shuttle bus North Railway Station line to North Railway Station for CNY 25 (about 50 minutes). Then, take a bullet train to Huashan North Railway Station (about 30 to 40 minutes). A second class seat costs CNY 54.5; a first class seat costs CNY 89.5. upon arrival, take bus line 1 or 2 to the mountain. :)