Rules: Dragon Guarded Sites

When a dragon becomes a guardian, it creates a geographical feature with an area of about 1 square mile per 5 points of Constitution the dragon had. The feature created always resembles a dragon in some subtle manner. The contours of a hill might suggest a sleeping dragon, for example, or a lake might have the shape of a dragon’s head or footprint.
Dragon eggs laid in a guarded area become hidden by nondetection and mirage arcana effects, provided the female laying them is of the same kind as the guardian. Both effects lasts until the eggs hatch, and neither effect has a magical aura, but otherwise they function as the spells cast by a 20th-level caster. Any dragon of the same kind as the guardian and of juvenile age or younger can visit the area once a month and receive the benefits of a commune spell. Older dragons of the same kind as the guardian get the same benefit, but only once a year.
The heart of a guarded site may indeed contain a small amount of treasure left over from the guardian’s transformation (hidden near the heart of the site). Such a treasure contains coins and goods only and is of a level equal to one quarter of the guardian’s Challenge Rating at the time of its transformation. Removal of the treasure does not harm the guarded site, but most dragons take a dim view of such activity.