Mountain Trail, Mountain Path
A mountain road is a mountain road! Or a mountain trail, or a mountain path.
Both the kanji in this word use the kun'yomi, which you learned when you learned the vocabulary. When it uses this reading, it sounds casual, and is common in conversation. It can also be read using the on'yomi, though, in which case it has a more formal feel to it. That's typical of on'yomi, which tends to add formality to a word!
Walking on a mountain path requires physical strength.
There are many turns on this mountain road, so always keep your feet on the brake of the car.
There are many weeds and insects on this mountain road, so please don't come with tank tops, shorts, or flip-flops.