GTA V had Mt Chiliad. RDR2 had the Grizzlies. GTA 6 has - Florida. The highest natural point in Florida is Britton Hill at 345 feet. There aren't going to be mountains.
We work through what elevation actually exists on the map and what 'high ground' means in this context.
Why there aren't mountains
Florida is geologically flat. The state is a sedimentary platform with very little elevation change. A GTA 6 map faithful to Florida cannot have mountains. The trailers consistently show flat-to-rolling terrain.
A 'mountain' in Leonida might be a low hill or a ridge - 100-200 feet of relief at most. That's not a mountain in the GTA V sense.
What might pass for elevation
Inland sandy ridges. The artificial high ground around developed areas. Construction-site mounds. Maybe a quarry or two. None of this gives the kind of vertical play that GTA V's Mt Chiliad supported.
The named place 'Mount Kalaga' has appeared in some community discussion. Whether it's official or fan-attributed is one of the things we're not yet sure about - we cover it cautiously.
What the lack of mountains changes
Aerial gameplay is different - no mountain BASE jumps. Photography is different - no Vinewood-Hills-overlooking-LS shots. Story-wise, classic 'mountaintop confrontation' set pieces aren't an option.
What replaces the mountain content is probably water-based and rooftop-based content - boat chases, bridge confrontations, high-rise sequences. Different vertical vocabulary.