The phrase "groups of hills" is correct and usable in written English.
It can be used to describe multiple clusters or collections of hills in a geographical context.
Example: "The landscape was dominated by groups of hills, each offering a unique view of the valley below."
Alternatives: "clusters of hills" or "sets of hills."
Elevations there generally are less than 1,000 feet (300 metres), but isolated groups of hills reach heights of 2,500 feet (750 metres) or more.
The relief is characterized by the low mountain ranges of the Aimorés Mountains on the western border and by isolated groups of hills on the eastern coastal plains.
Groups of hills rise from flat or slightly undulating country, and in the central parts are treeless plains covered with cogon grass (used for thatching).
In such random marks, Leonardo, who surely had a powerful imagination, could make out "landscapes adorned with mountains, rivers, rocks, trees, plains, wide valleys, and various groups of hills".
"If you are about to invent some scenes, you will be able to see in it a resemblance to various different landscapes adorned with mountains, rivers, rocks, trees, plains, with valleys and various groups of hills".
Isolated hills and groups of hills also protrude from abyssal plain surfaces, and the base of an abyssal plain accumulation of marine sediment, as revealed by sub-bottom seismic profiling, generally matches the undulating topography and relief of abyssal hill provinces.
There are two groups of hill forts in Cheshire, each with three members, but Maiden Castle is the outlier, about 9 mile south-south-west of the southern-most group.
This hill, Palatine Hill, was one of a group of hills, traditionally counted as seven, around which the ancient city grew.
Seven Hills of Rome, group of hills on or about which the ancient city of Rome was built.
The trachyte used in the Renaissance walls was extracted in the quarry district of the Euganean Hills, a group of hills located near Padua formed by a sedimentary succession of limestones and marls of the upper Jurassic lower Oligocene, a Paleogene volcanic and hypabyssal series, and Quaternary detrital deposits.
In the sector occupied by 1st Commonwealth Division, Chinese communist forces were dug into a group of hills overlooking the Imjin River.
