140 Cri. LOEMAN: 
undrained, or feebly drained areas, corresponding to Hill’s definition, 
exist par excellence. Here there is little danger of confusing soft 
Cretaceous strata with the later fill. 
The following list showing the depths of a few typical wells in the 
southern bolson region is compiled from a large number of logs 
furnished me through the courtesy of the Southern Pacific engineers 
and others. As the wells are sunk only to a good flow of water, 
the depth of the fill is not known in any case. The Esmond well 
is especially interesting, as it is situated toward the eastern edge of 
the semi-bolson of the Tucson District, about five miles from the 
nearest rock slope, and yet it shows 1,480 feet of typical outwash 
material. These wells indicate surely more than a ‘thin veneer” 
of detrital outwash. 
Well Depth, Feet Character 
Saftondessvesawelleie steer 1,820 Bolson lake beds 
Benson S. P. well No. 2... 7 Chiefly bolson lake beds 
Benson S. P, well No. 3... 806 Chiefly bolson lake beds 
St. David’s Artesian well... 530 Chiefly bolson lake beds 
Fsmond rss 2: .welle ee: 1,480 Tucson semi-bolson deposits 
Gilatse bs welltcrpercree: 1,386 Semi-bolson. Lava flow from 1,250 to 1,290 
Casa Grande S. P. wells... 615 A semi-bolson in Santa Cruz drainage in 
625 a region of typical bolsons 
Sentinel S. P. well, No. 1. 1,129 Showing 1 lava flow in section 
Sentinel S. P. well, No. 2. g62 Showing 2 lava flows in section 
Sentinel S. P. well, No. 3. 1,082 Showing 2 lava flows in section and all 
three are typical wash deposits of a semi- 
bolson region 
Wellton S. P. well........ ; 1,120 A semi-bolson near Colorado River 
The word ‘“‘bolson”’ of course is of Spanish origin, and its apph- 
cation by the early Spanish settlers and their descendants shows a 
keen eye for topographic forms, painfully lacking in the later American 
invader, who with perfect unconcern will, for instance, designate the 
surface of a topographic basin as a mesa (a table). 
In looking over a collection of old maps of the southwest at the 
Carnegie Desert Laboratory, I find that ‘“ Bolson Mapimi”’ appears 
on Thompson’s New General Ailas No. 50, published in 1814, and 
since then the word has been in continuous use as a technical geo- 
graphical term. Hill’s definition is faulty in that it imposes a restric- 
tion which is only possible of application after the geological structure 
9 Publication 99, ‘The Carnegie Institution of Washington, pp. 58, 59. 
