Remarks in Helena, Montana
It is a great pleasure to come through this State and to see legibly written for the most unobservant to read assured promise of a future greatness. I sometimes think that you yourselves do not altogether realize how great that future will be. Your mines count for much; your ranches count for much, but most of all is going to be done by the water, and in two ways. In the first place, thanks to the rapid fall of the rivers from the mountains, there is a well-nigh inexhaustible source of power in your streams, which will certainly be used in the building up of great manufactures. We are going to see great manufacturing centers here in Montana taking advantage of the power of your waters. In the next place those waters will be used under wise schemes of irrigation until you make this whole state blossom like the rose.
You need first of all to distribute the water in space through the irrigating ditches, and then to preserve it in time by storage in reservoirs, so as to keep the floods that run to waste of one season for use at the season when they are most needed. And Congress, the National Legislature, has not of recent years put upon the statute books any law as wise, as beneficent as the National irrigation act of a year ago. It was the beginning of the scheme of using aright the waters which have been allowed to go to waste, and, as all of you know, when irrigation becomes an accomplished fact, and the waters are used in accordance with the right principles of irrigation, we always find that rainfall is a very poor substitute for it.
We have passed in irrigation the stage of preliminary experiment. There is no question of what can be done by it. The question merely is as to the method, as to the means of making it most effective, and, in my judgment the greatest development within our borders, the greatest development not on the sea coast of the United States during the next half century will be the development of what have been called the arid and semi-arid lands under the application of the principles of irrigation. And I say one thing with emphasis, in endeavoring to secure the adoption of the irrigation law I was met with protests from people dwelling in the humid regions, who believed that the building up of agriculture in an intensified form in the arid regions through irrigation would be detrimental to them.
Theodore Roosevelt, Remarks in Helena, Montana Online by Gerhard Peters and John T. Woolley, The American Presidency Project https://www.presidency.ucsb.edu/node/343691