请高手语法分析下,连词while用的是否正确?

题目

请高手语法分析下,连词while用的是否正确?
While usually thought to end in northern New Mexico,the Rocky Mountain really extend southward to the frontier of Mexico.

答案

是个从句省略的形式宾语的句子即省去“it is",while表转折,“尽管”.整句是“While it is usually thought to end in northern New Mexico,the Rocky Mountain really extend southward to the frontier of Mexico”