Petra;

Your magnitude is not out of line for that area. The 1892 quake in that region shook a large area, and took down a number of buildings in the desert region. The records of the event are scarce.

USHIS 1892 02 24 0720 32.55 -115.63 7.76 MwHHT

Here are a couple of sites regarding the Laguna Salada region. I have been there and it is a large salt flat subject to ephemeral water stands during heavy winter rains. This water evaporates quickly, with summer temperatures well over 100 degrees. Some of the best work on the area has been done by Becky Dorsey, University of Oregon. She has also done work on the Western Salton Trough, a stones throw from home.

http://darkwing.uoregon.edu/~rdorsey/LagSal.html

http://www.uoregon.edu/%7Erdorsey/rjd.html

glen