Contextually the mist that went up was a phenomenon which happened during the week of creation, specifically on the third day. However, in conservative Christian doctrine this condition persisted until the time of Noah.
A Mist Went Up
March 3rd
Where did the water come from which watered the surface of the land? it up welled at Eden. Now, here's the real question, how did the water get to Eden if there hadn't been any rain?