This is an example of the geology and climate of Rosentia Island. I'm including this just so you can see how another writer sets up their world, what information they include or track down, etc. As I'm no geology student, some of this may be slightly off but I won't be quoting this in the novels itself so that should be okay.
Climate Region: Warm temperate. Temperature in winter averages 16C during the day and 6C at night with a risk of frost in low-lying areas. Temperature in summer averages 30C during the day and 20C at night with a risk of heat waves (generally high 30s due to coastal winds) for weeks at a time in the world-equivalent of January/February. This most often occurs when the weather comes down off the northern Ihlander salt plains. The mean sea surface temperature varies from 14C in winter to 19C in summer.
Ecological Regions: There are three primary biomes in Rosentia Island: scrubland, open forest, and coastal. Scrubland dominates the rockier, wind-swept regions to the west and center of the island. Open canopies of predominantly eucalypt forests cover the rolling hills in the outer and more eastern areas of the island. The coastal biomes obviously dominate the beaches.
Geological History: The granite that makes up Rosentia Island formed 10 km below the surface of the earth around 480 million years ago. The granite formed when layers of sediment were folded by the extreme pressure in the world’s crust alongside melting of the base rock by the extreme heat. Rosentia Island was located at a weak point in the world’s crust – a weak point formed by the footprint of an ancient spirit when it leapt from this world to the cosmos – which gave room for the molten rock to force its way upwards to the surface where it cooled and hardened into granite. Sediment has been layered over this land on a number of occasions, often linking it to the greater land mass, but a war between the weather spirits, sparked by the greed of a tidal princess for the storm prince’s electrical crown, caused the gradual erosion of the land, both exposing the granite beneath the dirt and eroding the land link between Rosentia Island and the main land.
Geography: The island is 14.7 kilometres long (2 hour walk) and 9.5 kilometers wide (1.5 hour walk). Large swathes of the south and west coastline are filled with steeply sloping granite cliffs. Along the north, particularly the north east, there are sandy surf-beaten beaches. The north-west Flycatcher Bluff (so-named after the old glass house of a long-dead Rosentia lady who grew carnivorous plants within) has an old lighthouse that overlooks the Shipgutter Cove whose rocky shallows consume any ship that ventures too near.
The ocean shelf in this region experiences cool-water non-tropical flows and these conditions favour growths of carbonate-producing bryozoans, coralline algae, sponges, molluscs, and asteroids. Much of the ocean shelf surrounding Rosentia Island is rocky but the region to the west has more pronounced granite features due to more severe weathering due to tidal / wind strength differences and due to the original geologic formation though the tidal influences is greatly reduced inside the cove. The original granite formation occurred less commonly to the eastern coast of Rosentia Island and this has allowed for a safer approach for ships and other vessels. There is also less severe weathering on the eastern side allowing for greater sediment build-up, a richer top soil, and thus more arable land.