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Message: <blockquote data-quote="mythusmage" data-source="post: 2351608" data-attributes="member: 571">A Rough Guide to DesertsDeserts come about for three reasons; latitude, blocking, distance. The Sahara in North Africa came about because of wind patterns. Moisture laden air stopped reaching North Africa soon after the end of the last Ice Age and things dried out. The Mojave on the other hand is a desert thanks to mountains. Back when the continents were clumped together into Pangaea the center of the supercontinent was a desert because it was real far from the ocean.Coastal deserts are possible when said coast lies next to a cold water current, and humid air is kept away. The Nazca in South America and the Skeleton Coast in Africa are examples of this. In the case of the former humid air from the east is blocked by the Andes, in the case of the latter the Skeleton Coast lies at the right latitude. The cold water currents help to make the situation worse. The Galapagos are another example of a cold water current combining with latitude to produce desert terrain.Where high altitude forests lying next to low altitude desert are concerned, Southern California is a lousy example. Taken as a whole the average rainfall is low enough to qualify the area as a desert. Trouble is, Southern California is not homogonous in terms of terrain and climate. A better example would be the state of New Mexico. The New Mexico desert has mesas scattered throughout and is bordered by low mountains. The high ground gets more rain and as a result can support forests.Then you have an altitude related phenomenon known as "virga". Virga is rain that doesn't reach the ground. Around here (San Diego CA) virga tends to evaporate before it gets below 5,000 feet.What this all means is that yes, you can have an island with forested mountains at either end and an arid lowland inbetween. All you need are mountains high enough to catch the rain that would otherwise evaporate before hitting the ground.There are additional complications, but this should cover the basics.</blockquote>

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