Please answer a question about the following article about Appalachian Mountains:

Before the French and Indian War, the Appalachian Mountains laid on the indeterminate boundary between Britain's colonies along the Atlantic and French areas centered in the Mississippi basin. After the French and Indian War, the Proclamation of 1763 restricted settlement for Great Britain's thirteen original colonies in North America to east of the summit line of the mountains (except in the northern regions where the Great Lakes formed the boundary). Although the line was adjusted several times to take frontier settlements into account and was impossible to enforce as law, it was strongly resented by backcountry settlers throughout the Appalachians. The Proclamation Line can be seen as one of the grievances which led to the American Revolutionary War. Many frontier settlers held that the defeat of the French opened the land west of the mountains to English settlement, only to find settlement barred by the British King's proclamation. The backcountry settlers who fought in the Illinois campaign of George Rogers Clark were motivated to secure their settlement of Kentucky.

Where did the mountains lay before the French and Indian War?
on the indeterminate boundary between Britain's colonies along the Atlantic and French areas centered in the Mississippi basin