In trail and road construction it is very often necessary to build bridges. Sometimes a very simple log bridge meets the need, but in bridging many large mountain torrents, which become very high and dangerous in the spring, large bridges are necessary. Cable suspension bridges and queen and king truss bridges are built where occasion arises for them, but only after being planned in detail and after the District Forester has approved their design and method of construction.
[Illustration: Figure 14. A typical Forest ranger's headquarters. Idlewood Ranger Station, Arapaho National Forest, Colorado]
Very often navigable streams and lakes are used as a part of the transportation system on a National Forest. On the Tahoe National Forest in California launches are operated by the Forest Service on Lake Tahoe to patrol the region around the lake for forest fires. Ferries, boats, and launches belonging to private companies or individuals are used by agreement or if necessary are bought by the Service from the Improvement funds. Speeders, motor cars, and hand cars on railroads or logging roads are often used when an agreement has been made with the company. In this way railroads are made a part of the transportation system of the Forest.
_Communication Facilities._ The system of communication on the National Forests is scarcely less important than the system of transportation. This system includes telephone lines, signal systems, and mail service. The telephone system, as can be readily seen, is of the utmost importance for the transaction of all kinds of National Forest business. In case a Forest Ranger wishes to speak to his Supervisor about controlling a large fire, it makes a great difference whether he can talk to him over the telephone or whether he must send a messenger on horseback perhaps 60 or 70 miles. In the former case practically no time is lost, in the latter it would take at least two days for the messenger to reach the Forest Ranger, and in the meantime the fire would continue to rage and spread.
In the absence of a telephone system a signal system is used. The one probably used the most in forest fire protection work is the heliograph, by which code messages are sent from one point to another by means of a series of light flashes on a mirror. The light of the sun is used and the flashes are made by the opening and closing of a shutter in front of the mirror. Very often these heliograph stations are located on mountain tops in the midst of extremely inaccessible country. Where there are a number of these stations at least one is connected by telephone to the Forest Supervisor's office. When the Forest officer at the telephone gets a heliograph message about a certain fire he immediately telephones the news directly to the Forest Ranger in whose district the fire is located, or if he does not happen to be in direct communication with the Forest Ranger he notifies the Forest Supervisor, who then notifies the officer concerned. Of course it is all prearranged who should be notified in case a fire is reported to the heliograph man.