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e e to be operated in a network configuration over a wide area. Thus, access to the barrier top and around it is very important. Practical access to mountain regions, including the transport of equipment and supplies, is possible by three means. . These are, in decreasing order of practicality and economy, truck on all-weather road, oversnow vehicle (snowmobile) and helicopter. Helicopter transport is necessary where roads or trails do not exist for truck or oversnow vehicle travel. Helicopter use is expensive; moreover, it is impractical during bad weather. However, installation and maintenance of seeding generators at remote, high-altitude sites often require helicopter tral)sport. Mountain observatories have been maintained during winter by oversnow vehicles, particularly where heavy equipment and stores can be transported in by truck during the summer or fall. Of course, the most economical and flexible situation is offered by all-weather roads and four-wheel drive vehicles, but few mountain regions have such access. Even where roads exist, travel to some equipment (e.g., precipitation gauges) usually is by oversnow vehicle. Consequently, rugged terrain with steep gradients, areas with high avalanche hazard, and heavily forested areas without trails, should be avoided in experimental area selection. Travel by motorized equipment, including helicopters, is prohibited in wilderness areas and in some parks and other recreation areas. In addition, operation 'of even simple mechanical equipment such as precipitation gauges is not allowed in wilderness areas. Consequently, all wilderness areas are unsuitable for the planned direct detection experiments. Wilderness areas may be operationally seeded in the future, as several are at present. However, the inability to operate observing equipment eliminates many of the high elevation regions of the Colorado River Basin from consideration as experimental areas. Another, perhaps obvious, experimental area requirement is that it have high elevation terrain; that is, mountains. All else being equal, a higher elevation experimental target area is better. The main reason is an enhanced frequency of SLW cloud cold enough for nucleation. A large fraction of winter storms appear to be too warm for llI'ound-based seeding with AgI. This is a particular problem in the southern portions of the Basin, and at lower elevations. Wherever practical, ground-based seeding is much preferred to airborne seeding because it is far more economical, and is practical during periods with strong winds, turbulence and heavy icing, all of which hinder aircraft safety. Even aircraft equipped for flight into known icing conditions cannot stay in a heavy icing environment (often corresponding to large seeding potential) for a prolonged period. Consequently, the direct detection seeding experiments will emphasize ground-based seeding. This technique appears to offer the most cost-effective alternative for increasing water production in the Upper Colorado River Basin. Two types of seeding agents will be used during the experimental propane, silver iodide (AgI) and propane. Seeding with propane (or any substance that chills the air below - 400C) can nucleate ice particles between 0 and about -80C where conventional types of AgI generators and solutions appear to be ineffective. During some storm stages, SLW is frequently warmer than -80C near many mountain barriers. Ground-based propane 3