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0[;0340 ,. westerly direction to the Colorado-New Mexico state line south of Ki m . The two basins differ considerably, as the study will develop, both from the source of their basic water supply and the controlling factors effecting ~he economics of irrigated agriculture. With the exception of l1mited surface and alluvial water suppl1es from the North Fork of the Republ1can River, Arikaree River and the South Fork of the Repub- l1can River, all of the northern basin's supply of water is from the Ogallala forma- tion. The aquifer varies from a fingeredge on the westerly edges of the basin to variable thicknesses up to 400 feet on the east. Saturat ed thickness varies from o to in excess of 350 feet with extreme variables in some areas because of irregular bedrock elevations. Although transmissivity varies, for the most part yields are primarily a function of saturated thickness. The Southern High Plains has a multiple aquifer development with very limited irrigation from surface suppl1es from Bear Creek and T1.I'O Buttes Creek. The Ogallala foOllation in this basin is quite limited and from a practical point of view is currently uneconomic for irrigation supplies because of little original satu- rated thickness, depletion, or loss to the lower aquifers because of early improper- ly completed wells. The other formations supplying water are the underlying Dakota, Cheyenne, and Dockum sandstones. Unlike the aquifer to the north, these forma- tiens are quite tight and the combination of limited yields and depth to pumping water level are the limiting factors controlling the irrigated agriculture in this basin. Institutional Status Both of the basins indicated above as Colorado's portion of the regional Ogallala study have been deteOllined to be "Designated Ground Water Basins" as defined in the Colorado Ground Water Management Act of 1965. The northern portion or area, deSignated in 1966, is known as the Northern High Plains Desig- nated Ground Water Basin and the other, designated in 1967, is known as the Southern High Plains Designated Ground Water Basin. These basins are adminis- tered differently from the historic surface streams and waters tributary thereto in other parts of the state. , In 1965, the Colorado Legislature passed the "Colorado Ground Water Management Act." This statute was the first effort by a Legislature to deViate from the strict priority, first in time is first in right, concept of the Colorado Constitu- ' tion. The Legislature said in its declaration of policy"... While the doctrine of prior appropriation is recognized, such doctrine should be modified to permit the full economic development of designated ground water resources. Prior appropria- tion of ground water should be protected and reasonable pumping levels main- tained, but not to include the maintenance of historical water levels. (emphasis added) All deSignated ground water in this state is therefore declared to be sub- ject to appropriation in the manner defined in this article." This is from Article 90, Title 37, C.R.S. 1973. In order to accomplish the purpose of the statute the Colorado Ground Water, Commission was created and consists of representatives from the designated basins', -4- -' .)'-