Geology and Soils
The Harris Fire burn area is underlain by primarily granitic plutonic rocks with some metamorphic rocks in the southwest portion (see Geology Resource Report for more detail). Soil types are composed primarily of four soil groups (NRCS, 1973):
1. Cieneba-Fallbrook Association, Very Rocky
Excessively drained to well-drained coarse sandy loams and sandy loams thathave a sandy clay loam subsoil over decomposed granodiorite: with 9 to 75% slopes. This association occurs in the Foothills and is made up of soils that developed in material weathered in place from decomposed tonalite or granodiorite. Erosion hazard is high to very high.
2. Exchequer-San Miguel Association, Rocky
Well-drained silt loams over metavolcanic rock; 30 to 75% slopes. This association is occurs in the Foothills and is made up of soils that developed in hard metavolcanic rock. Erosion hazard is moderate to high.
3. Rock Land Association
Dominantly exposed bedrock and very large boulders. This association occurs in the Mountains and Foothills, and is 50 to 90% exposed bedrock and very large boulders.
4. Friant-Escondido association, eroded
Well-drained fine sandy loam and very fine sandy loam over metasedimentary rock; 30-70% slopes. Erosion hazard is high to very high.
5. Las Posas association, stony
Well-drained stony fine sandy loams that have a clay subsoil over decomposed gabbro; 9 to 65 % slopes.
The high percentage of the Rock Land Association soil group is likely a contributing factor to the overall low to moderate burn intensity of the Harris Fire.
GEOLOGY MAP LEGEND (units within the fire perimeter)
Qya - younger alluvium of Quaternary age
Qoa - older alluvium of Quaternary age
Tf - fan deposits of Tertiary age
To - Sandstone and claystone of Miocene Age
Ksp - Santioga Peak Metavolcanics of Early Cretaceous Age
Kc - Cuyamaca Gabbro of Early Cretaceous age
Kcm - Corte Madre monzogranite of Early Cretaceous age
Kjv - Japatul Valley tonalite of Early Cretaceous age
Kmgp - Monzogranite of Mother Grundy Peak of Early Cretaceous age
Kgm - Tonalite of Granite Mountain of Early Cretaceous age