Here's the Height Map:
Just right click it and save it as OasisTerrain.png and place it in your terrains folder.
The biggest black blob is where the most water will be and I was thinking it would look nice if water falls flowed into it off of the edge white half circle in the upper right corner. The small dark grey dots are hiding spots and so is the larger one (:
Here's the Mask:
Right click it and save it as OasisMask.png in your terrains folder.
When I tested this I found that it looked very nice with the Red being Greengrass, the blue being Seasand and the green being Brownsand. I put the green in there to make it some sort of a path.
If anything needs to be changed please tell me! I made the map a bit bumpy to give it some depth (: