This (AmE) native speaker's reaction is that it's ordinary grammar, and a slightly poetic way to summarize the most salient facts about Death Valley.
Extreme can be an adjective or a noun. The plural extremes indicates that Death Valley has more than one kind of extreme condition—and they are all devastating. The extreme conditions referred to include weather conditions, but possibly other kinds of conditions (see below). The plural also suggests to me that some of the extremes might even be opposite to each other (which turns out to be true; see below). Devastating here means that the conditions are so extreme that they can kill people or cause enormous damage—possibly on a large scale or across a wide area.
Here are some facts about Death Valley:
It is one of the hottest locations on the surface of the Earth. During the day, the air temperature regularly goes over 120 °F (50 °C). It has been measured as high as 134 °F (56.7 °C), approximately the highest ever recorded anywhere.
Even the daily low temperatures in Death Valley are the highest on Earth. One night, the lowest temperature reached was 110 °F (43 °C).
The climate is extremely dry: the annual precipitation is only about 2" (51 mm).
When it does rain, the water sometimes creates ephemeral lakes—large, shallow lakes that quickly evaporate in the heat, leaving behind salt flats.
Death Valley has the lowest elevation in North America: 282 feet (86 m) below sea level.
It also has a high mountain peak: 11,043 feet (3,366 m).
I did not know any of those facts about Death Valley until I looked them up on Wikipedia just now. But the phrase devastating extremes, in the context of a sentence about Death Valley, vaguely suggests to me "those sorts of extremes".
The word devastation makes me think of images like this—which just happens to be a picture of a salt flat in Death Valley.