The volume of a cone with a radius of 100 feet and height of 25 ft is:
261,799.3877991494 cu ft = 9,696.27362 cu yd

Just a rough estimate, not taking flat bottom and 3:1 slope into account. (sorry at work and don't have a lot of time)

Last edited by DMRBG; 06/01/12 01:21 PM.