If province has "Mountain" mark in description - it`s mountain, sure
If there`s mountains on map, but no "mountain" terrain type in description - you may surprise, but it`s...right, it`s NO mountain
Also I always check first - with any type of easy scan, which is possible to my mages (e.g. Auspex, Gnom Lore etc.), and then (late, with good gem income, which I can trade to pearls) scan with Acashic Record. Some rare and powerful locations possible to detect only with ARec - and just one site with recruitable Trolls, Crystal Castle, Loremasters or powerful magic bonus can change balance to your side in no time