another option...تیغه is better for ridge, I think. See Google images for examples.

no exp.

hillock پُشته
Clay ridge خرپُشته‌ی رسی

No need to argue over "hillock", but let's deal with "ridges"!

In the below link, you can see a man walking over a mountain ridge.
http://www.google.com/imgres?q="mountain ridge"&um=1&hl=fa&s...

A definition for "ridge": the long narrow top of a mountain or group of mountains (McMillan dictionary)

In my opinion, "ridges" here refers to the long narrow top of those hillocks. It is called "ستیغ" in Persian. You can google "ستیغ کوه ها", and you'll find many of its examples.

آتشگاه ها بیشتر در جای های بلند و بر ستیغ تپه ها و کوه ها بر پا می شده اند، و کاربرد آن در مواقع خاصی بود که آتش بر آن ها قرار داده می شد،
http://mirasyar.persianblog.ir/post/60/

However, it can also refer to a range of hillocks or mountains. Please notice the following definitions:

1. a range of hills or mountains (Merriam Webster Dictionary)
2. A long and narrow hilltop, mountain range, or watershed; a range or chain of hills or mountains; a line or reef of rocks (Shorter Oxford Dictionary)

For this definition, you can translate it as "رشته تپه های رسی" or "رشته ارتفاعات رسی".