How do the people of mountainous regions fast and pray, and what fatwa did Ibn Baz issue concerning this?

If the inhabitants of mountainous regions are in a high place where they can see the sunset, the matter is clear. However, if they are in a low place where they cannot see the sunset, they deduce the entry of the Maghrib time and the breaking of the fast by the arrival of darkness from the East, and the absence of any sunbeam on walls or mountain peaks. Al-Nawawi said: "The beginning of Maghrib time is when the sun sets and its setting is complete." And our companions said: "The consideration is the complete disappearance of its disk... As for populated areas and mountain foothills, the consideration is that no trace of its rays should be seen on walls and mountain foothills, and darkness should approach from the East." Al-Hattab said: "As for a place where it sets behind mountains, one looks towards the East, and when darkness appears, it is an indication of the sun's setting."