Question

请帮忙理清一下这句话中的主句谓语动词，从句谓语动词以及非谓语动词的时态关系

A group of people moving slowly down the Mackenzie River valley east of the Rockies into the general region of Southern Alberta, then eastward across the northern prairies reaching the wooded county around the upper Mississippi and the Western Great Lake, then in a southeastward movement following the Mississippi valley until some final settlement was reached in the Gulf states, would encounter a wide variety of physical environment.

Answer 1

主句应该是a group of people（主） ....would encounter（谓）....其余皆为修饰成分。
moving。。。into一句是现在分词做伴随状语，
estward、southward引导的都是状语成分，本身应该是副词词性。
eastward一句中reaching是现在分词做目的状语。
southeastward一句中following也是现在分词，此句中有个从句，由until引导的结果状语从句，其中final settlement是主语，was reached谓语。
个人意见，欢迎指正。

追问

谢谢，你的语法结构分析不错，我更想搞清楚其时态关系，能否用时态的语言再深度解析一下，呵呵

追答

主句would encounter无法看出时态，但从southeastward一句中的从句谓语动词was reached可看出是一般过去时。非谓语动词是对现实情况的一般陈述故在此句中也是一般现在时，没有其他时态。