340 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1959 
a study of what goes on in some of our mirage-forming layers, pro- 
vided we knew where the layer was and further provided that very 
light winds cooperated to let the balloon and instruments stay where 
wanted. 
The second distortion pattern shown, the Portal Mirage (fig. 3), is 
a much less formal one and, in my experience, much less frequent. It 
may appear quite suddenly. Its invariable habit of leaving passage- 
ways between the built-up hill masses is characteristic and suggests the 
name. It is not flattopped and does not send out streamers. The 
normal hill profile seems rather to be lifted and partially flattened 
out. Its height, in the same group of hills as Flattop, differed very 
little. In a recently observed case, the area of the temperature-in- 
version layer, at least the effective part of it for mirage building, 
must have been quite small and moving. Buildup started at the west 
end of the line of hills and moved eastward, building as it went. Be- 
fore the east end of the line had been reached, westernmost hills were 
back in normal shape. It causes one to wonder why, once or twice a 
season perhaps, the Flattop routine is interrupted for a day by this 
pattern. 
Ficure 3.—The Portal mirage. This is a considerably less common form than Flattop, 
in the writer’s experience, but based on the same group of hills. Its behavior is much 
more informal than Flattop’s, often much more hurried in the making and unmaking. 
Streamers do not seem to be any part of its pattern. It seems to keep some of the skyline 
of the hill, considerably flattened and lifted. It has the invariable habit of leaving pas- 
sageways between the hill masses, hence its name. 
A very different type of distortion was observed from my lookout 
hill in the early spring of 1951. Some 75 or 80 miles to the south- 
east, across the broad delta plain of the Colorado River, rises the 
Cocopah Range some 1,800 to 8,000 feet high with skyline only gently 
irregular, with no noticeable peak. On this particular morning, less 
than an hour after sunrise, the sky was heavily overcast with alto- 
stratus clouds, making it an unusually dark morning for this desert 
country. Well off to the southwest there must have been a break 
in the clouds, not showing, but letting a shaft of sunlight through. 
The mirage makers had been really busy. It looked as if they had 
scraped together all the material in the 50-mile-long Cocopah Range 
and piled it up into a great Fujiyama-like peak well over twice as 
high as the range itself. The shaft of sunlight spotlighted this 
mountain and it shone splendidly, like a vision, the only bright spot 
in a dark and gloomy world. I watched it for 10 or 15 minutes 
through binoculars. The range to right and left was completely 
blotted out, as if a dirty whitewash brush had been drawn through 
that part of the picture. In spite of the distance, such brightness 
