因为形容词修饰表示度量的名词应后置 ,即数词+名词+old (long,high,deep,tall名词等）如
a.The building is seventeen storeys high.
b.He is ten years old.
c.We had to climb over the mountain that was five hundred meters high.
因此,歌曲继承这种用法,如river deep mountain high,是一种省略用法 是为了上口,但是不正式.
关于for you 的成分,由于没有上下文,不敢妄自乱说,如果有上文,接逗号,很可能表原因,做因为讲,与上句是并列句.