While the number of reported storms is too small to warrant a discussion of their geographical distribution in the United States, the above table so far, no doubt, correctly represents the facts that it shows an increase from the Western plains to the Pacific coast, and comes to a maximum in the Southwest. On the plains most places are reported to experience dust storms two or three times in a year, while on the Pacific coast estimates and records for different places range considerably above this number. At Los Angeles, Cal., one observer says that there are "two or three in the course of a year, possibly a few more." From Yuma, Ariz., the statement comes that "any high wind, without rain, generally blows clouds of dust," and six sand storms were recorded by observer A. Ashenberger in the Weather Bureau station at that place during 1893. At Ontario, Cal., it is estimated that there are from twelve to forty dust storms in a year. It is said that these storms are "most common and strongest in passes in the mountain ranges in California," that they are "very severe on the east side of the Coast Range," and that "nearly every part of California is afflicted [by them] at times." From the reports which are at hand an estimate of the minimum frequency of these disturbances in places in the West, where topographical and climatal conditions do not forbid them, is two in a year for the territory east of the Rocky Mountains and five in a year for the Great Basin and the western slope. A maximum estimate would be four annually for the former region and twenty for the latter.
Data on the areal extent of each separate storm are meager, as reports of simultaneous observations have been secured in but few instances. Where such observations have been reported they represent, as is evident, the minimum extent of the storm in one direction, since it may have extended beyond the points from which the reports have come. The few instances of reported areal extent of dust storms may be tabulated as follows:
Areal Extent of Single Storms.
|From||Milton, Ore., to Colfax, Wash.||80||miles.|
|"||Fresno, Cal., to Santa Maria, Cal.||120||"|
|"||Mojave, Cal., to Oceanside, Cal||140||"|
|"||Salem, S. Dak., to Sanborn, N. Dak||216||"|
|"||Santa Anna, Cal., to San Diego, Cal||270||"|
|"Over the greater part of Nevada"||300||"|
|Over most of northern Iowa and Illinois||400||"|