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employed in evaluating other project purposes. Nevertheless, the National Park Service has provided a measure of the benefits by using "A method of Evaluating Recreation Benefits of Water Control Projects," which it adopted in August 1957 and updated in February 1963. This method provides for a monetary evaluation of the benefits to the individuals visiting the area. On a national basis, the evaluation has been determined to average 52 cents per visitor day for general public use, including picnicking, swimming, and sightseeing; an additional 55 cents per visitor day for boating and water skiing; and an additional 50 cents per visitor day for camping. methodology assumes that all visitors will pay a general use fee. Visitors engaged in boating and water skiing or in camping are assumed to pay additional fees for these activities. The construction of the Bridge Canyon Dam and Reservoir will create three recreation resource use conditions: (1) it will generate new and additional general recreation opportunities not previously available in the immediate vicinity of the project; (2) it will eliminate a 93-mile stretch of wild river which presently supports some four to five hundred raft or float trips per year; and (3) will utilize the lower 13 miles of the Colorado River within the Grand Canyon National Park as a reservoir. Benefit-cost estimates can be applied against the first result. The second condition represents a decrease in, but not the complete elimination of , a current recreation use. It will result in a decrease of more than one-third of the length of wild, free-flowing river available for river-running in the Grand Canyon. The third project effect (reservoir invasion or encroachment within an established National Park) gives rise to intangible considerations. These intangibles can best be treated as a basic policy issue, rather than as a problem in benefit-cost determination, even though the cost of avoiding the encroachment can be calculated in terms of other economic benefits forgone. Because of the above admixture of factors, the Bureau of Outdoor Recreation has agreed to an arbitrary limitation of annual benefits to no more than the annual cost of providing the specific recreation facilities, which is $629, 500. At Marble Canyon Reservoir, scenic boating will be of such unusual and unique quality as to require special consideration in selecting a benefit value for this activity. Accordingly, a relatively higher value of $5.00 per water-borne sightseer is considered a reasonable estimate for such use at Marble Canyon Reservoir. The annual benefits and costs for Maxwell Reservoir are based on assumed additional Federal development of recreation facilities 4Epson Perfection 4870 Photo, 400 dpi, 8 bit, 13,670,400 byte