Adobe was one of the primary building materials used in many of the Missions as well as other early settlements. In fact, the Native Americans had been using Adobe for hundreds of years before the Spanish came. Adobe was used because it got the job done (provided building material to create dwellings) and it was cheap and easy to make.
Adobe is made primarily out of clay, soil (dirt), small pebbles and rocks, straw, grass, sticks, and other materials at hand. One could liken Adobe to the concrete of today: The mud formed from clay and soil mixed with water forms a cement, the pebbles and rocks are like the aggregate in concrete, and the straw, grass, and sticks could be related to steel rebar.
After the raw adobe mixture was made, it was molded into bricks which were left to harden in the hot sun for several days. Then, they were used just like bricks to build buildings. The bricks were held together with a mortor, often made in a similar was as the raw adobe was made.
Project Idea: Create your own adobe and make some bricks, or make a small-scale model of a Mission.