138 
IOWA ACADEMY OP SCIENCE 
In central New Mexico there is an extensive chain of saline lakes lying on 
the Estancia plains, that admirably illustrate the case in hand. Viewed from 
a distance of five or six miles the Estancia lake-district appears as a group of 
prominent hills rising like islets out of the broad expanse of level plain. Upon 
approaching the hills there is suggestion of low volcanic ash-cones with their 
characteristic truncated tops. The hills rise abruptly a hundred to a few hun- 
dred feet above the level of the surrounding plain. The materials composing 
the hills is white or gray, yielding, and of the appearance of volcanic ash. On 
ascending these fiat-topped elevations the central portions of each are found to 
be depressed as deeply as the level of the plains outside. To all appearances 
each is a crater-lake. But there are not the slightest traces of volcanic action 
either in or near the lakes, not even in the neighborhood within a distance of 
many miles. There are no outlets to any of the lakes. The inner walls of the 
lake-basins are very steep, frequently forming cliffs. 
The bottoms of the basins are usually covered by snow-white films of alkali 
or salt, the water having completely evaporated, so that one may even walk 
across from one shore to the other. At times the water is said to be eight to 
ten feet deep; but this only happens once every three or four years. 
The “craters” are essentially sand-dunes, or rather clay-dunes, formed under 
unfamiliar conditions. A stiff breeze blows most of the time over the plains. 
As the bottom of the lakes become dry after rain, the gypsum, alkali or salt 
coating cracks in the sun into sandy material. The moist clay beneath does 
the same thing, first curling up into thin leaf-like plates. This material the 
winds blow about over the dry lake bottom and finally carries it up and out 
of the basin over the rim, where it falls on the leeward side. Almost any time 
one may see the sands and pulverent loam stream up over the inner walls of 
the depressions, which have an angle of about 40 degrees, and form a drift a 
foot thick in an interval of a few minutes. As the winds come from every 
quarter of the compass during the month and year each truncated hill develops 
in a fairly even manner. If anything the northeast side shows some advan- 
tage. 
No vegetation grows within the depressions. The sands and loams are light 
and loose whenever the lakes become dry, and most of them are in this condi- 
tion for the greater part of the year. Outside of the rims plant-growth, which 
abundantly covers the surface of the plains, also reaches up the hillsides to the 
summits and protects the dry pulverant materials from the free action of the 
winds. Within a short distance there are contrasted the extremes of differen- 
tial wind action upon areas well protected by vegetation and those not thus 
protected. 
The noteworthy fact to be taken into consideration in the present connection 
is the crater-like character of the loam-dunes in the middle of a broad, open 
plain. These conspicuous hills are rarely more than a mile across, though they 
may be sometimes several miles in length, as in the case of the Laguna del 
Perro, four miles east of the town of Estancia. In a similar manner irregular 
dunes are formed of enormous size on the alkali fiats of other parts of New 
Mexico. The famous white sands district, in the Hueco bolson, 100 miles to 
the south of the Estancia region, may be cited. These dunes are of pure gypsum- 
sand and have the appearance of huge piles of granulated sugar. They are 
often fifty to sixty feet high. 
