A stream of thick, viscous lava flowed slowly out of an opening at the southern base of Cinder Cone. As the lava crept down the gentle slopes of the valley, it crusted over, forming a black, slag-like surface. The surface was from time to time broken up and mixed with the softer portions beneath, so that the movement of the flow was still further retarded. At the lower end of the valley the lava occupied a portion of a body of water now known as Lake Bidwell; its rugged front made a dam across the valley above, forming Snag Lake. The stumps of the trees which were killed by the water when the lake was first formed are still standing. [Illustration: FIG. 29.--THE LAST LAVA FLOW IN THE UNITED STATES At Cinder Cone, California. It formed a dam across a valley, thus creating Snag Lake] One's feet sink deep into volcanic sands, and walking is tiresome. The lava field resulting from the last eruption is free from sand, but its rough surface, formed of broken blocks, is difficult to cross. A few charred stumps rise out of the sand, pathetic remnants of the forest trees that were growing at the time of the first eruption. Most of the trees have completely disappeared, leaving shallow pits where they once stood. It is exceedingly difficult to climb the cone, which rises over six hundred feet, for the slopes, composed of loose lapilli, are so steep that one slips back at every step nearly as far as he advances. From the summit a remarkable sight meets the eye. Within the rim of the main crater is a second crater with a rim nearly as high as the first, while the cavity within has a depth of about two hundred and fifty feet. Because of the loose character of the material of which it is built, no streamlets have yet worn channels down the slopes of Cinder Cone, and except for the presence of two small bushes which cling to its side, it is just as bare and perfect in form as when first completed. Little by little the forests are encroaching upon the sand-covered slopes about the cone, and in time these slopes, the black fields of lava, and the cone itself, will be covered with forests like the older lava fields and cinder cones which appear upon every hand. THE MUD VOLCANOES OF THE COLORADO DESERT The Colorado Desert is a strange, weird region. Here is a vast basin at the head of the Gulf of California which was once a part of the gulf, but is now separated from it by the delta of the Colorado River. With the drying up of the water, the centre of the basin was left a salt marsh more than two hundred and fifty feet below the level of the ocean. In summer the air quivers under the blazing sun, and it seems as if no form of life could withstand the scorching heat, but in winter the atmosphere is cool and full of life-giving energy.