292 REPORT UNITED STATES ENTOMOLOGICAL COMMISSION. 
Mountain Valley and Huerfano Park. West of the Sangre de Cristo 
Range lies the large valley of San Luis, beyond which is the broad and 
complex group known as the San Juan Mountains. These ranges are 
all covered with forests to the timber line. The Wet .Mountain Valley 
is timbered except in the lower part near the Arkansas River, where the 
plateaus, into which it develops, are well grassed. The Huerfano Park 
has a very similar vegetation, being timbered near the divide and on the 
minor ridges, while grasses cover the lower parts. 
The San Luis Valley, which contains the upper course of the Rio 
Grande, is a long valley, extending from Poncho Pass down into New 
Mexico. It has a length of about 140 miles, a maximum width of fifty, 
and an average width of 35 or 40 miles. Its area is not far from 5,300 
square miles, of which about two thirds is in Colorado and the balance 
in New Mexico. Its surface is almost as Level as a billiard table. In 
the northern part the growth is bunch-grass. As we proceed southward 
it changes very gradually to sage, which in turn becomes more and 
more stunted, and in the soul hern part of the valley the vegetation is very 
scanty, excepting at the bases of the ranges on the sides. The soil, too, 
undergoes a corresponding change from a gravelly soil at the northern 
end and at the bases of the mountains on the sides. Farther down the 
valley, about Sawatch Creek, the soil becomes a stiff adobe clay, and yet 
farther down the valley it becomes very sandy. In some places along 
the eastern side of the valley the sand has heaped up in drifts or dunes. 
This is notably the case near the Music and Mosca Passes. The sand 
begins near the latitude of the point where the Rio Grande enters the 
valley, and extends down to its southern end. 
There is quite a large area of marsh and semi-marsh in the northern 
portion of the valley. San Luis and Sawatch Creeks entering the val- 
ley near its northern end, join and flow down the valley near its eastern 
border, and sink in the San Luis Lakes, near Mosca Pass. Their course 
in the valley, and especially below their point of junction, is sluggish and 
accompanied by a broad belt of marsh and of land naturally irrigated. 
About the lakes this area is much enlarged. 
The San Juan Mountains contain no valleys of any extent. Baker's 
Park, an area of possibly half a dozen square miles, is the only bit of 
flat country to be found among them, except among their lower spurs, 
which will be noticed farther on, under the head of the Plateau area. 
Proceeding southward into New Mexico, we find the lower limit of 
timber crowded higher and higher up on the mountains, so that, on the 
lower ranges of the southern part of the State, there is no timber what- 
ever. 
The low range of the Ratons on the boundary between Colorado and 
New Mexico is well timbered, though grasses extend well up its slopes. 
The Sangre de Cristo Range is covered with forests to its end, near San- 
ta Fe, and the Sandia Mountains, a short group which continues its 
course for a few miles southward, are also well timbered. East of the 
