This is the 17454th most frequent Polish word.
zasypanych
"Zasypanych" means "covered" or "buried" (typically under something like snow, sand, or debris).
Here, 'zasypanych' is a past participle used as an adjective describing the fields, denoting being covered (or buried) by snow.
Dzieci bawiły się w śniegu, rzucając się śnieżkami na zasypanych polach.
Children played in the snow, throwing snowballs on the snow-covered fields.
In this case, 'zasypanych' describes the debris, emphasizing that they are covered with or buried under something after an event like a collapse.
Strażacy znaleźli rannego człowieka w zasypanych gruzach po zawaleniu budynku.
Firefighters found an injured person in the buried debris after the building collapsed.
Here, 'zasypanych' describes the canyons, indicating that they are filled (or buried) with sand.