It is quite common to see cairns at high points in Mongolia. They can be at the peak of a hill or mountain or at the crest of a pass. A cairn is basically a pile of stones with a few sticks standing out in the centre with coloured prayer flags adorning the structure. They are considered holy and some Mongolians honk thrice when passing them. It’s a way of thanking God for getting them up to that point. If they are on foot it’s customary for them to walk around the cairn, pick up a stone and throw it onto the pile while saying a short prayer.
People also leave stuff at the cairn. In these pics you can see a crutch at the base of the cairn. Most probably the owner had met with an accident and used the crutch for a while. After getting cured he must have walked up to this cairn, left the crutch there and prayed for something like that to never happen again to him.