The new building was to be constructed by Civilian Conservation Corps (CCC) personnel living at the CCC camp on the south side of the mountain.  Company 2932-V (World War I veterans) started work on the summit building in 1938.  While plans for the new observation building were being finalized, a number of older structures were demolished and the are prepared for the new building that would house not only a viewing deck but also an aircraft beacon, a fire lookout, and the museum exhibits.  The new building was constructed from sandstone quarried at Fossil Ridge on the mountain.  Standard Oil of California donated money for the mortar, steel, and other materials need to complete the structure. 

Work on the new summit building came to a halt in 1940.  The exterior of the building was completed, however, a serious problem with water leaks during storms developed during the winter months.  Water would run through the mortar and sandstone into the interior of the building.  Several attempts were made to solve the problem over the next several years.  Although each solution helped, none seemed to totally resolve the problem. 

In the early 1950s, the Department of Parks and Recreation obtained several contracts to seal and complete the exterior of the building.  The mortar joints were sealed and pointed, the observation deck roof was resealed, Gunite was applied to the interior of the building   and the exterior of the building was sealed.  However, even this did not make the building entirely waterproof.      

The work on the exhibits was completed by the W.P.A. in 1942 and the finished panels and displays were transferred to Contra Costa County’s Hall of Records for safe storage until the summit building was completed.   When it became apparent that the leaks in the summit building would not be easily resolved, the displays were transferred to Mount Diablo State Park and stored at the recently abandoned Civilian Conservation Corps camp at Live Oak Campground.   In 1951, after completion of additional efforts to seal the summit building, park employees discovered that many of the displays and paintings had been damaged beyond salvage by water, rodents, and dust.  Those displays that could be salvaged were shipped to Sacramento where they were repaired and sent to other park units for use. 

The final blow for the summit museum came in 1956 when the temporary museum caught fire and burned to the ground.  The displays were lost as well.  Throughout the 1950s and 1960s interest in a summit building visitor center continued to come to the forefront; however, without the necessary leadership nothing happened. 

Then, in 1974, Mount Diablo Interpretive Association (MDIA) formed to promote public awareness of the cultural and natural history of Mount Diablo.  The members developed a temporary visitor center in a portion of the old summit building, staffing it with volunteers and docents.  As MDIA’s interpretive efforts grew they searched for ways in which the 40-year old dream of a museum and visitor center at the summit could be realized.    

In 1982, the California State Park Foundation, a non-profit organization dedicated to expanding California’s parks and recreational opportunities, joined forces with MDIA to help raise the necessary funding for the summit building project.  The next year, the Department of Parks and Recreation agreed to correct the water intrusion problem and prepare the structure for exhibits and displays.  Daniel Quan Design of San Francisco developed the plans for the museum and visitor center.  Installation of the exhibits was completed in 1984. 

Today, the museum and visitor center house a diorama of the park’s ecosystems, complete with the sounds found in nature, and a topographic model of the mountain.  On one wall, an instructional video and lighted display case describes the geologic forces that created the mountain.  On anther wall, cultural history is chronicled with splendid photographs.  The lower level of the summit building contains panels describing the Native American history of the region and an audio-visual room.  Rotating displays of art and photography complement the permanent exhibits.  In addition to the exhibits, there is a small gift center within the building.   

Outside the summit building, telescopes are mounted on the observation deck.  A close-up view of the Delta and the surrounding geology is just a quarter.  On a clear day, the Sierra Nevada can be seen with the naked eye.  If you look carefully, ancient marine fossils embedded in the sandstone walls can be seen along the stairway walls leading to the observation deck.   The rotunda on top of the summit building is a reminder of Mount Diablo’s importance as a survey point.  Sitting atop the rotunda is the old navigation beacon, lighted once a year on December 7 in memory of Pearl Harbor.