Burned Area Emergency Response (BAER) Assessment FINAL Specialist Report – GEOLOGIC HAZARDS Dolan Fire Monterey Ranger District Los Padres N.F. October 9, 2020 Jonathan Yonni Schwartz – Geomorphologist/Geologist, Los Padres NF Introduction: The Dolan Fire started on August 18, 2020 and was 98% contained as of October 8, 2020. The fire burned on the Monterey Ranger District of the Los Padres NF, as well as across the Fort Hunter Liggett military reserve camp, State Parks, County and private properties. Out of a total of 124,327 acres, 82,311 acres burned on National Forest Lands, 29,063 acres burned on the Fort Hunter Liggett military camp lands, 1,880 acres were burn on State Park lands and 11,074 acres burned on private lands. Out of a total of 124,327 acres, 12,362 acre were high soil burn severity (10%), 56,257 acres were moderate soil burn severity (45%), 45,047 acres were low soil burn severity (36%) and 10,688 acres were very low soil burn severity or unburned (9%). The unburned acres refer to unburned areas within the fire perimeter (Figure 1). This report describes and assesses the increase in risk from geologic hazards within the Dolan Fire burned area. 1. Objectives: When evaluating Geologic Hazards, the objectives of the “Geology” function on a BAER Team are identifying the geologic conditions and geomorphic processes that have helped shape and alter the watersheds and landscapes, and assessing the impacts from the fire on those conditions and processes that potentially could affect downstream values at risk (VAR’s). The fire removed vegetation that helps keep slopes and drainages intact, changed the structure and erosiveness of the soil, and altered the stability of the landscape. Using the understanding of rock types and characteristics, geomorphic processes, and distribution of geologic hazards helps predict how the watersheds will respond to and be impacted by upcoming storms. 2. Initial Concerns: Human Life and Safety: • People living, working, traveling or recreating through and below burned areas – Loss of life or injury could take place as a result of debris slides, debris flows, rock- fall, or flooding in and downstream of the burn area. 1 Property: • Forest Service roads, trails and campgrounds, CA Hwy 1, State Parks roads, trails and other facilities, County roads, private access roads – As a result of the fire, excessive runoff and flows are expected, stability of slopes over roads, trails and other facilities is compromised. Debris slides, debris flows, rock-fall, and flooding could cause damage to these systems. • Residential houses and other structures, water systems, and other properties - As a result of post-fire conditions, excessive runoff and sheet flows are expected, stability of slopes is compromised. Debris flows, rock-fall, and flooding could cause damage to this infrastructure. Natural Resources: • The Wildlife- Fisheries BAER Assessment evaluated risks to four federally-listed fish and wildlife Values at Risk which could potentially be impacted by the fire or by post-fire effects; 1) California condors, 2) SCCC Steelhead DPS and designated critical habitat, 3) California red-legged frog and designated critical habitat, and 4) Smith’s blue butterfly. It was determined that the fire could potentially impact all of these species in various ways. • Landslides, debris flows, and mass wasting events have potential to impact populations of steelhead and California red-legged frogs and their critical habitat either directly or indirectly. Direct impacts could include injury or mortality, while indirect effects include degraded suitable or critical habitat conditions, degraded water quality, or habitat alteration resulting from increased sediment loads deposited in the creek channels by debris flows or landslides. • Smith’s blue butterfly are likely at greater risk of direct or indirect impacts to individuals or habitat due to landslides or mass wasting events. Suitable habitat for the species occurs along the western slope of the frontal range of mountains, on both sides of Hwy 1, and may be negatively impacted by mass wasting and landslides which are common in this steep terrain following wildfires. • Risks to condors are primarily related to direct effects from the fire itself, and the cumulative impacts of large recurring wildfires on roosting habitat. They are unlikely to be impacted by geological-related events. Cultural Resources: • The burn area is prehistorically attributed to the Salinan and Esselen tribes who occupied the area prior to European contact and settlement. In the mid-eighteenth century this area began to be influenced by Spaniards and later Euro- Americans. Mission San Antonio de Padua (1771), is located only 1 mile from the fires most eastern extent. 2 • Initial concerns include adverse effects to numerous site types representing both prehistoric and historic periods. Most site types are prehistoric and include rock art, intact midden deposits, lithic production sites, milling stations, and habitation sites. Historic era sites are represented by the Spanish mission period and early homesteading with associated grazing and agriculture as well as early forest preserve and forest service management. • Of immediate concern is identifying cultural resources at risk resulting from a reduction in surface vegetation and compromised soil structure by deteriorated post-fire conditions. Surface and subsurface cultural depositional context that has vital scientific or interpretation values may be altered or lost by increased runoff, erosion, and debris flows during inclement weather within deteriorated watersheds. Increase in runoff and debris, can also expose cultural resources, subjecting them to risk from vandalism and theft. Figure 1: Soil Burn Severity map of the Dolan Fire area 3 3. Resource Condition Assessment: Resource Setting – Physiology and climate: The Dolan Fire occurred in the Santa Lucia Mountain Range, within the Coast Ranges geomorphic province. The Santa Lucia Mountain Range is about 140 miles long, extending from Carmel in the north (Monterey County) to the Cuyama River in the south (San Luis Obispo County). The physiography of the Santa Lucia mountains is characterized by northwest-trending, steep-sided, sharp-crested ridges that paralleling the numerous faults that transect the area and are separated by youthful V-shaped valleys (Pearson and Fillo, 1967). All associated watersheds flow directly or indirectly into the Pacific Ocean. The topography is complex, reflecting active uplift and deformation, a variety of lithological types, rapidly incising stream networks and highly unstable slopes. Stream channels and hillslopes are very steep, with average hillslope gradients exceeding 60% in some sub-watersheds. The coastal side of the range rises directly from the shoreline, with oceanfront ridges rising directly 4,000 to 5,000 feet to the crest ridge. The climate gradient in the range is likewise extreme, reflecting the coastal position and steepness of the range. The coastal ridge may exceed 100 inches of rainfall during the winter wet season, while the eastern portions of the area may average less than 20 inches of annual precipitation. This drastic climate gradient is due to the rain shadow effect of the range, which blocks the prevailing southwesterly approach of most Pacific cyclonic storms. Little to no precipitation occurs throughout the range during the dry summer and fall seasons under the prevailing Mediterranean climate. Bedrock Geology and Structure: The basement rocks of the Santa Lucia Range, within the burned area are predominately comprised of Paleozoic Salinia Block (“Salinian Block”) metamorphics. Other rocks in the area, to a lesser degree, include: Cretaceous Great Valley Group, Mesozoic Franciscan rocks, and alluvium (Figure 2). The Salinian block is made up of highly fractured, and deeply weathered meta-sediments, especially biotite schist and gneiss, intruded by plutonic (granitic) rocks such as quartz diorite and granodiorite. The Great Valley Group is an ancient forearc system that is comprised of mudrock, sandstone, and conglomerate that preserve a record of Farallon-North American plate convergence throughout the Cretaceous period (Surpless, 2014). The Franciscan complex is composed of greywacke sandstone and greenstone, with serpentinite bodies and other ultramafics present. Isolated areas of marble and limestone form resistant outcrops that are prominent landscape features, usually white to light gray in color. 4 Surficial Geology: Steep slopes within the metamorphic rocks indicate that the un-weathered rock beneath the surface soils is not deeply weathered. However, within the granitic rocks, the slopes can be very steep even though the underlying granitic bedrock is deeply weathered. Road cuts in these granitics can usually be cut very steep, such as 1/4:1 to vertical without becoming unstable. Quaternary to recent landslide scarps and deposits are common in many areas within the burned area. Alluvial or debris flow deposits are preserved in a few areas, although little valley-fill has accumulated in the steep, narrowly incised canyons. In many drainages, deposits from previous floods and debris flows have been washed of finer sediments, leaving large boulders and cobbles exposed. The burned area has been disrupted and tectonically slivered by Quaternary motion on the San Andreas fault zone. The Sur, McWay, Coast Ridge, Nacimiento, Junipero Serra and Arroyo Seco faults are prominent Quaternary features influencing the linear NW/SE