There are spots on the great plains where, if you are on the highest ground, you can see clearly for miles and miles.  People on the plains relied on the clear air and their vision to alert them that something was moving toward or away from them.  Sometimes this was life and death information.  The dry conditions allowed dust to rise from the slightest disturbance.  The larger the movement, the more voluminous the dust.   Sort of like a primitive radar, but giving you much more information.