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longer route by way of Tubac and Tucson) the main overland tributary to "El Camino Real'"-The Royal Highway of California.

The Jesuits were expelled in 1767; but the old Yuma trail and the old California missions remained as monuments to their enterprise and as means of later progress.

With the international friction presaging the Mexican war, the importance of the ancient trail began to wane; with the treaty of Guadalupe Hidalgo in 1848 our own argonauts cast their eyes toward the far-rumored overland route, and with the gold fever of Fortynine the activity along the fitly named Camino del Diablo waxed again temporarily. The sharing of its miseries by American and Mexican adventurers begot sympathy and mutual understanding, and opened enduring friendships which helped to heal the international breach and obliterate the scars of warfare. Yet the transitional epoch was not without painful episodes; the Crabb filibustering expedition struck the historic trail on their way via Sonoyta, to be annihilated at Caborca (where the old church still bears bullet-marks of the battle); tradition tells of an immigrant colony from Mexico to California following the ancient way to Tinajas Altas, where they were halted by an evil conjunction of epidemic with international complications to fill literal scores of graves still dotting the barren footslopes of the dazzling sierra; and equally stirring events still live in the memories of all older Arizonians and Sonorenses.

It was during the gold-fever renaissance that the death-roll of El Camino del Diablo became most appalling, for many of the travelers were fresh from humid lands, knew naught of the deceptive mirage or the ever-hovering thirstcraze of the desert, and pressed out on the sand wastes without needful preparation. The roll will never be written in full, since most of the unfortunates left

no records, scores leaving no sign save bleaching bones; but observers estimate that there were 400 victims of thirst between Altar and Yuma within eight years, an estimate which so conservative a traveler as Captain Gaillard thought fair after he had "counted sixty-five graves in a single day's ride of a little over thirty miles."


With the Gadsden purchase of 1853, the boundary surveys already under way received fresh impetus, while the belated argonauts still trying all possible paths toward the new territory, whose


was synonymous with gold for a generation, were once more tempted southward. So, even before the survey reports were published the fame of the route spread widely; stories of hard marches over the malpais stretching out from the volcano of Pinacate, of the miring of outfits in the bottomless mud of Tule valley in springtime, of wagons clogged in shifting sands, of desperate night marches under the sharp goads of thirst and hunger, of rescues of thirstcrazed waifs, of burials of the bodies and distributions of the goods of less fortunate parties-these and other heartrending recitals were whispered afar, or penned in friendly letters, to color the lore of America's most energetic pioneering and filter meagerly (far too meagerly for full history) into literature. The ill-repute of the trail gradually diverted the overland travel to more northerly routes, and when the Southern Pacific Railway pushed over the arid zone in the seventies the old route was finally deserted, save by Papago pilgrims in the sacramental journeys still pursued, and by rare prospectors or hunters.

The final chapter in the history of the Yuma trail touches only the retraversing of the route (after sixteen years without the passage of a vehicle) by the International Boundary Commission of

1891-1896, and the erection of the most serviceable series of international boundary monuments on the western hemisphere-massive pillars of cast iron or solid pyramids of cement-laid stoneeach so located that the next monument and the intervening country in either direction can be seen from its site, while the position of each is established with respect to neighboring natural features by published photographs. The boundary party was of men well known throughout both countries; the American commissioners, Colonel Barlow, Captain Gaillard, and Astronomer Mosman, like the naturalist, Dr. Mearns, were chosen on account of previous achievements, while the Mexican commissioners, Señores Blanco, Gama, and Puga, were equally eminent representatives of the sister republic. A report worthy to serve as a model for future commissions, accompa

nied by an ample atlas and a portfolio of photo-mechanically faithful portraits of the plains and mountains intersected. by the boundary, has been published within a few months, while one of the clearest pictures of the arid region ever drawn is Captain Gaillard's "Perils and Wonders of a True Desert."*

The wheel ruts and mule tracks left by the party seven years ago are still plain along the trail, save where obliterated by sand-drifts; even the tent-pegs, ashheaps, half rusted cans, and empty pickle bottles still attest the arduous work and

*The Cosmopolitan, October, 1896, pp. 592–605.

frugal fare of the commissioners and their colaborers; for one of the characteristics of the desert is the extreme sluggishness of surface-changing processes, a sluggishness hard to realize by those who dwell in humid lands.

After the passing of the boundary parties, the old trail remained untrodden from Quitobaquito westward, except by a road supervisor erecting guide-posts in the portion lying within Yuma County, and by three horsemen (an American, a Mexican, and an Indian) in other portions, until November, 1900, when it was struck by an expedition of the Bureau of American Ethnology.

Such, in brief, is the history of one of the most striking and picturesque routes of travel on the continent. Trodden first in a prehistoric period known only through crumbling ruins, then fol

lowed for half a millennium or more in votive journeys of Papago tribesmenthe Bedouin of America-it was traced by Spaniards long before the landings on James' island and on Plymouth Rock. Adopted by evangelists two centuries ago, it soon became a line of pioneering, a highway of colonization, an artery of royal communication; next it was thronged by the indomitable army of argonauts on their way to open a new world on the shores of the Pacific, and later it lapsed into utter desert, than which there is none more forbidding in America.

To be concluded in the April number.



ROM May to September little rain falls in San Francisco, but every afternoon great banks of fog march in from the Pacific and enwrap the houses, streets, and hills in their dense folds.

Ocean fogs as a rule form when cool air flows over warm moist surfaces; but in the case of the San Francisco sea fogs these conditions are reversed, for the ocean surface temperature is 55° Fahrenheit, while the air temperature may reach 80°. Another explanation, therefore, of the cause of these fogs must be sought.

A glance at the map (not reproduced) shows how ocean, bay, mountain, and foothills are crowded together. East of San Francisco stretches a valley 450 miles long and 50 miles wide and level as a table. In this valley the afternoon temperature in summer is usually 100° or over. The valley is connected by a narrow water passage, the Golden Gate, with the Pacific Ocean, the mean temperature of whose waters is in this locality about 55°. Thus within a distance of 50 miles in a horizontal direction there is frequently a difference of 50 degrees in temperature. At the same time in a vertical direction there is often a difference of 30 degrees in an elevation of half a mile. Well-marked air currents, drafts, and counter-drafts are therefore prevalent

The prevailing surface air currents at this season of the year are strong westerly currents, but high bluffs, ridges, and headlands intercept these winds at such an angle that they are diverted to and pour through the Golden Gate with greatly increased velocity. The result is that both air and water vapor are piled up at this point. Mr. McAdie therefore

*An abstract of a paper contributed to the Monthly Weather Review for November, 1900, by Alexander G. McAdie, forecast official of the U. S. Weather Bureau at San Francisco.

concludes that the summer afternoon fogs of the San Francisco Bay region are probably due to mixture, rather than to radiation or expansion. They are the

result of sharp temperature contrasts at the boundaries of air currents having different temperatures, humidities, and velocities. In originating and directing these air currents the peculiar contours of the land also play an important part.

The fog outside the Heads may extend over an area 10 miles square and reaches to a height of about half a mile. If it were solidly packed its bulk would thus be 50 cubic miles. As a cubic foot of the fog at its average dew-point temperature, 51° F., weighs 4.222 grains, a fair estimate of its total weight, allowing for wide swaths or channels fog free, is 1,000,000 tons. This immense volume is carried through the Golden Gate by westerly winds blowing 22 miles an hour, from 1 to 5 p. m. on summer afternoons.

The United States Weather Bureau maintains a station on Mt. Tamalpais, which is about half a mile above sealevel and thus above the fog, another in the city of San Francisco, where the fog converges, and a third station at Point Reyes, the center of origin of the fog. fog. Mt. Tamalpais is about 25 miles from Point Reyes and 10 miles from San Francisco.

The differences in the temperature and humidity of these three stations is most marked. The highest temperature recorded on the mountain during the year 1899 was 96°, on July 18; the maximum temperature on the same day at San Francisco was 66°, and at Point Reyes 52°. That is, on the mountain it was 30 degrees hotter than in the city and 44 degrees hotter than at Point Reyes. The mean annual temperature of the three stations is, however, about the same for all, 55°, which is also the


Figure 1.-Morning Fog over Valleys.

View from U. S. Weather Bureau Observatory, Mount Tamalpais.


Figure 2.-Lifted Fog. Height above ground about 500 meters.

View from U. S. Weather Bureau Observatory, Mount Tamalpais.

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