This is the 16661st most frequent Russian word.
сибирской
"Сибирской" translates to "Siberian" in English, relating to Siberia.
Here, "сибирской" functions as an adjective modifying "шерсти" (wool), describing its origin as from Siberia.
Я купил шапку из сибирской шерсти.
I bought a hat made of Siberian wool.
In this case, "сибирской" modifies "реке" (river), specifying that the river is located in Siberia.
На сибирской реке летом можно увидеть много птиц.
On a Siberian river in summer, you can see many birds.
Here "сибирской" modifies "природой" (nature), emphasizing its characteristic as representative of Siberia.