The Harrap's New Shorter French and English Dictionary Ed. 1985, defines one of the senses of "knob" as an AmE equivalent for "knoll", i.e. a small, rounded hill or eminence; hillock.
Sadly enough, it doesn't say if this so-called Americanism was to some extent more commonly used back in the 80s than its shared synonym, nor if it ever caught on in AmE in that sense.
And so, I wish you could tell if "knob" for "knoll" has any currency at all in AmE today. Or does it sound unequivocally archaic to your ears?
The knoll upon which Jacksland stood overlooked the river, just a grassy knob that felt peaceful and untouched... source