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Section 779.19 (b) Continued, 1 J area will be significantly disturbed by mining. The three that will not be significantly disturbed are the Drainage Bottom, Salt Flat, and Exposed shale-gravel. The total area of disturbance for all of the three types will be less than 8 acres. Drainage bottom and Salt Flat will experience 2.43 acres of disturbance by proposed haul roads which will cross the Williams Draw and Bush Draw. On the Exposed Shale-gravel type, 5,46 acres will be affected. As previously agreed upon in discussions with OSM and MLRD, these acreages will be added to the Sagebrush-grass type for computation o£ the weighted average to be used in determining revegetation success as described in Section 816.116. Reference areas for each of the four vegetation types that will be significantly affected by mining have been established. Reference Area locations are given on Map 18, Kerr Mine Area Vegetation. Statistically, there was no difference between the premine sites and the reference areas, with the exception of the production para- meter for the grass component 1n the Alkali Sagebrush type (Table 30, Summary of Statistical Analysis). Here, the premine area was heavily grazed by cattle while the reference area received light grazing. Since the difference is in favor of the reference area, e.g., production was greatest for the reference area, it should be acceptable for future reference. Comparisons of production, cover, diversity, and the number of species in each premine area and reference area is presented in Table 29, Summary of Vegetation Types. Drill pads that were revegetated with a simple mixture of western wheatgrass and annual ryegrass were evaluated as an indication of the possibility of grass re-establishment by seeding. From the five pads tested, an average production of 359 pounds per acre and 21.9% cover was produced by 14 plant species, Range in production • values varied from 280 to 475 pounds per acre while range in per- 779-76