M EMORANDUM

DATE: OCTOBER 31, 2018

TO: Mr. William R. Short Acting State Geologist California Geological Survey 801 K Street, MS 12-20 Sacramento, CA 95814

FROM: Jeremy Lancaster (CGS - Acting Supervising Engineering Geologist) Team Lead

SUBJECT: Holy Fire Debris Flow Inundation Hazard Assessment within Riverside County

Cal OES Mission #: Deployment Date: 2018-SREOC-51612 September 9, 2018

Team Members (CGS): Jeremy Lancaster – Team Lead (PG, CEG) Don Lindsay – Co Lead (PG, CEG, CE, GE) Brian Swanson (PG, CEG) Pete Roffers (PG, GIS Support) Sol McCrea (CFM, GIS Support)

Introduction The Holy Fire began on August 6, 2018 in Holy Jim Canyon on the upper west flank of the Santa Ana Mountains. The fire burned 23,136 acres of land within Riverside and Orange counties before it was fully contained on September 13, 2018. Eighty percent (80%) of the burn area was within the Cleveland National Forest and the remainder was within private State Responsibility Areas or Riverside County. The fire destroyed twelve residences in Orange County and six more in Riverside County. Governor Brown declared a state of emergency for Riverside and Orange counties on August 9th.

A U. S. Forest Service (USFS) Burn Area Emergency Response (BAER) Team was mobilized to validate the Soil Burn Severity (SBS) map and to assess potential post-fire hazards and mitigation for areas under Federal responsibility (USFS, 2018). Most of the Holy Fire area had not burned within the prior 40 to 70 years and the BAER team found that 85% of the area burned at moderate or high severity soil burn severity, which is unusually high (Nicita and Halverson, 2018). The validated SBS map was submitted to the U. S. Geological Survey Mr. William R. Short October 31, 2018 Holy Fire Debris Flow Inundation Hazard Assessment Riverside County – Cal OES Mission Task No. 2018-SREOC-51612

(USGS) post-wildfire landslide hazards group, where models of potential debris flow probability and volume were generated for the Holy Fire on August 22, 2018 (USGS, 2018). This modeling indicates a high probability for debris flows in the major canyons within the burn area under expected rainfall intensities and for generation of substantial volumes of debris.

Due to the increased potential for debris flows and flooding under post-fire conditions and the presence of extensive residential development down-slope of the burn area, particularly in Riverside County, CAL FIRE mission-tasked a California Watershed Emergency Response Team (WERT) to assess potential Values-at-Risk (VARs). CAL FIRE and CGS led the response team with support from DWR, and the team coordinated closely with the USFS BAER Team and with representatives of the Riverside County Flood Control and Water Conservation District (RCFCWCD) throughout the response effort. The WERT identified 79 VARs and presented a summary of findings to Riverside County personnel at a close-out meeting on August 30 to assist in the county’s initial response planning efforts. The WERT report was finalized and posted on the CAL FIRE website on September 28, 2018 (CAL FIRE, 2018a). Most of the VARs identified by the WERT are within Riverside County.

Purpose and Scope Riverside County requested additional assistance through CalOES for CGS to prepare maps illustrating areas subject to high and low energy debris flow inundation in Riverside County, following the approach developed in the aftermath of the January 9, 2018 Santa Barbara debris flow event (see attachment in Thomas Fire WERT report (CAL FIRE, 2018b)). In response to the Cal OES mission task request, CGS assembled a team with a background in geomorphology and debris flow hazard assessmentPreli minar y , and GIS support personnel, to conduct the requested assessment.

CGS met with RCDCWCD staff on September 11, 2018 and agreed on the following scope of work:

• Task 1: Conduct field review and appraisal of existing available data. Identify and recommend acquisition of additional data. • Task 2: Review and provide input to preliminary hazard mapping developed by the county. • Task 3: Rapidly map the potential extent of debris flows and sediment-laden floods within and down gradient of the Holy Fire burn perimeter within Riverside County based on current conditions, including:  Distribution, age and type of alluvial fan deposits.  Identification and position of alluvial fan topographic apices, and possible hydrographic apices.  Presence of features on the landscape suggestive of past debris flow activity.  Map and catalog “accessible” locations that may impact the conveyance capacity of local channels (i.e. channel constrictions or “choke points”).  Consideration of event-based inundation. scenarios developed for downstream urbanized areas

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Mr. William R. Short October 31, 2018 Holy Fire Debris Flow Inundation Hazard Assessment Riverside County – Cal OES Mission Task No. 2018-SREOC-51612

• Task 4:  Assist Riverside County in the development of a decision matrix based on four levels of risk tiered to four different triggering rainfall events that could be used to support operational response decisions.  Develop recommendations for additional work  Develop this project report

Task 1 of this assessment began with reconnaissance field work from September 10 to 12, 2018, and was followed by discussions with the county and recommendations for additional information, including, high resolution lidar, aerial photography, and hydrology data. Task 2 was completed at the request of RCFCWD on 9/26/2018 by reviewing the “draft Holy Fire Risk Map” prepared by the county. After historic aerial photos of the area were assembled and lidar imagery was obtained and processed by RCFCWCD to produce detailed, post-fire topography, CGS completed Task 3 field mapping between October 10 through 12. An overview of geomorphic conditions by canyon and table of aerial photo review notes is attached in Appendix B and C, respectively. The results of the above listed tasks are included in this report and its associated attachments.

As with the January 2018 Santa Barbara County response, the primary objective of Task 3 is to rapidly identify channel constrictions where avulsions may occur during storm events and to qualitatively delineate areas of potential inundation by high and low energy flows. Procedures for this task include:

• Review of historic aerial photography to Prelie minar y valuate geomorphic expression of past flood and debris flow events in order to characterize recent flood and debris flow activity • Review of historic aerial photography and locations where manmade alterations may influence flow paths of debris flows. • Map and catalog channel constrictions (natural or manmade) or bends that may limit, or block, the conveyance capacity of local channels, which could force future flows out of their channels (avulsion) and generate debris flows and debris-laden flooding away from established flow paths. • Consideration of mapped channel constrictions and existing channel capacities by reviewing HEC RAS models at channel constriction locations. • Preparation of maps illustrating areas subject to potential high and low energy flows.

The purpose of this rapid approach is to provide a general understanding of the potential extent of debris flow inundation based on geomorphic factors. Quantitative modeling of potential flow paths was not a part of the scope of work.

Concurrent with the preparation of the qualitative high and low energy map, CGS provided assistance to Riverside County emergency management personnel, RCFCWCD, and CalOES in the development of a decision matrix based on four levels of risk tiered to four different triggering rainfall events that could be used by emergency response managers and personnel to develop appropriate operational needs and logistics. The rainfall thresholds in this matrix were based on published relationships from previous events, debris flow thresholds identified by the USGS for the Holy Fire area combined with input from the NWS, and input from Riverside County.

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Mr. William R. Short October 31, 2018 Holy Fire Debris Flow Inundation Hazard Assessment Riverside County – Cal OES Mission Task No. 2018-SREOC-51612

Background The following sections provide general background information on fire-induced effects on runoff and the unique characteristics and hazards associated with debris flows, mud flows, and flash floods. The observations and results obtained during this assessment are discussed thereafter. Discussions pertaining to the geologic, geomorphic, and climatic characteristics within the impacted areas and upslope source areas are provided separately in the WERT and BAER Team reports already completed for the Holy Fire (CAL FIRE, 2018a; USFS, 2018).

Fire-induced Impacts on Runoff Vegetation on natural, unburned slopes supports and protects the soil, creates a litter covered surface that acts to reduce raindrop impact and soil detachment, intercepts rainfall and provides evapotranspiration that reduces the availability of water to generate runoff. When the vegetation is burned during wildfires, the benefits provided by the vegetative cover are lost and runoff in the watershed is increased, both in overall streamflow volume and peak flow. Thus, post-fire flows are flashier than normal with more frequent flood events, especially in the first two to five years following a fire (Cannon et al., 2008; USGS, 2005). For this reason, post-wildfire runoff can be disproportionately large for the size of the watershed (Moody et.al., 2013).

In general, the denser the pre-fire vegetation and the longer the fire residence time, the more severe the effects of the fire are on soil hydrologic function. This is because aside from consuming vegetation and vegetative litter, fire can promote the formation of water repellent layers at or near the surface of soils which subsequently increases runoff. The two primary ways in which soil infiltration is affected by fire is by soil sealing and the creation of water-repellent (hydrophobic) soils near the surface. Soil sealing is caused by the infilling of surface voids in Preli minar y the soil by fine-grained clay and ash exposed and mobilized by raindrop impact after fire (Larsen et al., 2009). Hydrophobic soils are caused by the creation of a waxy substance that coats soil particles near the surface as hot vapors generated by the burning of organic matter condense in the cooler soils1. Fires can also disaggregate shallow soil particles, forming a mantle of cohesionless mixture of ash, sand and gravel. This material is subject to dry ravel processes on steeper slopes and results in increases susceptibility to surficial erosion both by rain and wind (e.g. Lamb et al., 2011). In debris flows, this material increases the density and viscosity of the matrix, enabling transport of boulders and other large debris.

Debris Flows, Mud Flows, and Flash Floods Post-fire debris flows, mud flows, hyperconcentrated flows and flash floods occur rapidly in response to high intensity rainfall events, are difficult to predict, and pose a significant risk to life and property. Research in recently burned watersheds indicates that rainfall durations of <30 minutes are most significant, with the 15-minute duration providing the most accurate prediction of post-fire debris flow generation (Staley et al. 2017).

Debris flows are high density mixtures of water, fine- and coarse-grained sediment, and debris that can form rapidly due to erosion or shallow landsliding during intense rain. Debris flows are high energy, allowing them to entrain cobble- to boulder-size material and trees, scour material from channels, and exert high impact forces. Debris flows also exhibit a substantially elevated, boulder-laden surge front. Debris flows that occurred earlier this year in Santa Barbara County

1 https://www.uidaho.edu/-/media/UIdaho-Responsive/Files/Extension/forestry/F5-After-the-Fires- Hydrophobic-Soils.ashx

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Mr. William R. Short October 31, 2018 Holy Fire Debris Flow Inundation Hazard Assessment Riverside County – Cal OES Mission Task No. 2018-SREOC-51612

serve witness to the destructive power debris flows can have. Mud and hyperconcentrated flows are not preceded by boulder-laden surge front, but have relatively high fluid density and energy, present a significant hazard to downstream population and infrastructure. Post-fire debris flows and sediment-laden flood flows travel rapidly, commonly exceeding 10 miles per hour.

Preliminary Debris Flows and Flood Hazards Map CGS designated inundation areas either as high energy zones, generally corresponding to areas subject to proximal, higher impact debris flows, and low energy zones corresponding to more distal and lower impact hyperconcentrated flows and mud flows. In addition, a buffer zone was delineated around the perimeter of the burn area where there is a general risk for hazards associated with steep slopes, such as smaller debris flows, hyperconcentrated flows, nuisance flooding, debris slides, or rockfall hazard. This hazard also applies to improvements located adjacent to slopes within the burn perimeter. The preliminary mapping effort and the resulting preliminary hazard zones (Appendix A) were based on field observations and best available information, including review of:

• Historic aerial photographs obtained for portions of the study area for the years 1953, 1962, 1967, 1969, 1974 and 1980 (see table in Appendix C for specific citations and observations) • Historic topography, including 1: 125,000 scale topography surveyed in 1897-98, 1: 62,500 scale topography surveyed in 1939-41, 1: 24,000 scale topography compiled in 1951, and RCFCWCD 4-ft contour topography compiled between 1958 and 1972 • Lidar acquired between 9/17 and 9/19/2018, associated hillshade and 4-ft contour products processed from the lidar DEM • High resolution imagery acquired with thePreli minar y Lidar on 9/14/2018, and review of Google Earth imagery • Infrastructure mapping by RCFCWCD, including drainage structures and buildings • Published geologic mapping of the area by Morton and Miller (2006) • The WERT report prepared for the Holy Fire (CAL FIRE, 2018a) • The BAER Team reports prepared for the Holy Fire (USFS, 2018; Nicita and Halverson, 2018) • Geomorphic conditions and current manmade improvements/alterations observed during the study • HEC RAS 100-year flood-flow modeling prepared by the RCFCWCD for Dickey, Horsethief, Cow, Indian, northern tributary of Indian, Coldwater, and Sycamore Canyons • A draft geomorphic assessment report for Coldwater Canyon conducted by JE Fuller (2018) • Pre-existing FEMA 100-year flood zones and DWR Flood Awareness Zones • Modeling of post-fire debris flow hazards by the USGS • Accounts of historic flooding from RCFCWCD personnel, local residents, and business owners

In our assessment of the 2018 Santa Barbara County debris flow event, the CGS team used the resulting debris flow inundation characteristics as a reference for the maximum event in developing the hazard map and decision matrix. Lacking this type of historic reference for the Holy Fire assessment, the CGS team reviewed HEC RAS modeling prepared by RCFCWCD personnel and JE Fuller (2018) and compared them with potential debris-flow-producing storm rainfall scenarios and debris flow bulking factors. Based on this comparison, the team found that the flow depths for a clear-water, steady-state 100-year flood-flow event provides a reasonable surrogate to evaluate the hydraulic capacity of the channels under bulked debris flow conditions.

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Mr. William R. Short October 31, 2018 Holy Fire Debris Flow Inundation Hazard Assessment Riverside County – Cal OES Mission Task No. 2018-SREOC-51612

For example, 2- to 10-year return period flows bulked by a factor of 3 to 4 and 25-year return period flows bulked by a factor of 1.4 to 1.7 is roughly equivalent to 100-year clear-water flood flows. This selected flow event was adopted to identify potential overbank flow and avulsion sites, including areas within the natural channel, areas influenced by manmade modifications (i.e. encroachment of fill and crossing structures), and observed post-fire mitigation measures, observed by the team as of October 12, 2018. The selected event criteria do not preclude the possibility that a more severe event, or cumulative set of events, could occur during the recovery period in the burn area.

Potential debris flow and sediment-laden flood flow paths on alluvial fans are dynamic and difficult to predict due to the distributary nature of fan channels, planform convexity of fan surfaces, evolving conditions on the ground over time, and variable response depending on the specific nature of a causative storm. Flow paths are particularly uncertain within the built environment, as debris flows may interact with channel blockages, structures and roadways. Consequently, the mapped areas of possible runout for both higher-energy flows (debris flow) and lower-energy (sediment-laden flood) shown on the hazard maps have a degree of uncertainty. Responsible agencies should re-evaluate channel conditions and capacity of existing mitigation measures immediately following any significant event and update response criteria as needed. The uncertainties in the current qualitative assessment could be reduced by conducting a quantitative debris flow hazard analysis.

It is notable that Riverside County, the City of Lake Elsinore, and private entities, have already implemented numerous emergency mitigation measures, such as the placement of K-rail deflection structures at previously identified at-risk channel crossings, construction of a large earth-fill levee to protect the homes and school at the mouth of Rice Canyon, removal/reconstruction of undersized crossing structuresPreli minar y along the channel issuing from Horsethief Canyon, and debris removal from the Coldwater Canyon channel adjacent to the Glen Ivy resort. These measures are expected to reduce potential impacts during a given storm event and the improvements observed as of October 12, 2018 were taken into consideration for the current assessment. However, many of the improvements were undertaken after the Lidar was acquired and therefore are not reflected in the associated topography or HEC RAS modeling provided for review. In addition, at the time of the field review, CGS did not observe mitigation measures of potential hazards in Indian Canyon, and the risk to previously identified VARs in this canyon remains high.

Channel Constrictions Channel constrictions (“choke points”) or bends are significant drainage features that can lead to avulsions, reoccupation of inactive channels, and flow along unexpected paths, such as roadways, resulting in potential inundation of areas far beyond established channels. This assessment therefore focused on identifying and assessing potential constrictions based on the WERT assessment, detailed mapping, HEC RAS 100-year flood modeling by RCFCWCD personnel, and review of aerial imagery and new lidar base maps and topographic contours developed from lidar. Mapping was conducted by a three-man team during an initial reconnaissance field assessment from September 10 to 12, prior to receiving the lidar, and during a second field review from October 10 to 12, 2018 when most of the requested lidar, imagery, and topography were in hand.

Information gathered and recorded at each channel constriction included:

• A two-part Site Identifier compiled to include a uniform abbreviation for the source

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Mr. William R. Short October 31, 2018 Holy Fire Debris Flow Inundation Hazard Assessment Riverside County – Cal OES Mission Task No. 2018-SREOC-51612

canyon area and a two-digit number for each station • The Latitude and Longitude of each channel constriction (NAD 83) • A brief summary of observations

Choke point locations are shown on the accompanying preliminary post-fire debris flow inundation hazard maps, and the information pertaining to each “choke point” listed above is summarized and provided in the attached maps (Appendix A).

Response Decision Matrix CGS assisted in the rapid development of a preliminary decision matrix based on four levels of response tiered to four different triggering rainfall events. The four response levels range in general risk from low to extreme and correspond to the following event characteristics:

Level 1 (“lower risk”): Runoff is largely free of debris and stays within the current channel network. Debris flow potential is negligible; potential for flooding is low for storms less than or equal to 1-hour duration and moderate for 6-hour durations or greater.

Level 2 (“moderate risk”): Runoff includes mud and some debris. Debris flow potential is low to moderate; potential for flooding is moderate for storms less than or equal to 1- hour duration and high for 6-hour durations or greater.

Level 3 (“higher risk”): Debris Flow Magnitude I to II (as defined in Cannon et al., 2010): potential is high for widespread small and moderate debris flows and potential for a

larger (> 10,000 cubic yard) debris flow; Prelipotential minar y for flooding is high for short and long duration storms. Overtopping flows and channel avulsion is expected at channel constrictions. Roads may be blocked. Structures within designated hazard zones may be endangered.

Level 4 (“extreme risk”): Debris Flow Magnitude III (as defined in Canon et al., 2010): Widespread abundant debris flows and flooding with volumes in excess of 10,000 cubic yards; potential for flooding is high for short and long duration storms. Debris flows and sediment-laden floods are anticipated to move out of channels and over the channel banks. Roads are likely blocked and considered unsafe for travel. Structures, particularly those within the designated hazard areas, would be endangered.

The triggering precipitation thresholds for each response level were then prescribed and are presented in the following Figure 1. It is important to mention that the Level 3 precipitation threshold was developed in consultation with the U. S. Geological Survey’s post-wildfire landslides team and the National Weather Service’s San Diego forecast office. The Level 4 thresholds were developed based on consultation with the County of Riverside as well as our understanding of field conditions present at the time of our assessment. It is recognized that field conditions will change if storm runoff and deposition occurs, or if additional mitigation measures are implemented to increase conveyance or debris basin capacity. As conditions change over time, the thresholds may be adjusted to better match the new conditions.

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Mr. William R. Short October 31, 2018 Holy Fire Debris Flow Inundation Hazard Assessment Riverside County – Cal OES Mission Task No. 2018-SREOC-51612

Preli minar y Figure 1: Precipitation depths and durations and emergency response levels.

The CGS team then prepared a preliminary matrix defining the rainfall event and corresponding debris flow magnitude and flooding potential to guide Riverside County in the preparation of a decision matrix.

The threshold between Level 1 and 2 was estimated as the rainfall that would produce primarily sediment-laden flows that may cause localized flooding, erosion, and debris deposition.

The threshold between Level 2 and 3 is the same threshold described by Staley et al. (2013) for the San Gabriel, San Bernardino, San Jacinto, and Santa Ana Mountains, and confirmed by Dennis Staley via email on August 28, 2018. Based on our discussions with the USGS and NWS, the NWS is using this threshold for flash-flood and debris-flow early-warning notification system for the Holy Fire.

Lastly, the threshold between Level 3 and 4 was set at the request of Riverside County to be equivalent to a storm event with a 25-year annual return interval. Thus, the threshold was calculated by averaging depth-duration-frequency data obtained using NOAA Atlas 14 centered over the watershed midpoint elevation in Rice and Coldwater canyons. The resulting 15-minute duration threshold closely matches that described in Cannon et al. (2010 for a Magnitude III event. However, in comparison, at longer durations the 25-year depths result in a higher event triggering threshold (i.e. greater precipitation depth over a given duration) becomes less conservative compared to that described in Cannon et al. (2010). This less conservative

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Mr. William R. Short October 31, 2018 Holy Fire Debris Flow Inundation Hazard Assessment Riverside County – Cal OES Mission Task No. 2018-SREOC-51612

threshold for longer duration storm events was evaluated and considered appropriate based on site-specific conditions, including: (1) the unique, elongated basin shapes that buffer storm events and result in a more attenuated flood hydrograph near the canyon mouths; (2) the presence of low-gradient, infilled channels with braided flow paths extending upstream of the fan apex that, under most flow conditions, allow deposition of course material to occur, as evidenced in the field; (3) the favorable performance of the channel systems within the upper fan elevations during historical floods; and (4) the recent improvements within high-risk channels to improve storage (e.g. debris basins at Leach and McVicker Canyons) and/or conveyance capacity (Horsethief, Rice, and Coldwater canyons).

Summary CGS was mission-tasked through CalOES at the request of Riverside County to conduct an assessment of potential debris flow hazards in Riverside County resulting from post-fire conditions resulting from the Holy Fire. CGS requested and received a series of historic aerial photos, HEC RAS 100-year streamflow discharge modeling, Lidar imagery and associated detailed topography from the RCFCWCD. The CGS team utilized these data to:

• Map channel constrictions, bends and other features that could impact conveyance capacity • Assess channel conveyance capacity at mapped constrictions • Prepare a preliminary map illustrating the potential distribution of high and low energy flows • Provide storm rainfall scenario guidance with proposed rainfall thresholds and Preli minar y corresponding debris flow response to Riverside County for emergency planning • Assisted responsible agencies in the development of a decision matrix based on four levels of risk tiered to four different potential triggering rainfall events

This preliminary memorandum provides a rapidly prepared brief account of the work done regarding the above tasks and presents the rapidly developed preliminary results as attachments.

As discussed, site conditions are ever evolving and new and revised data continually arise. For this reason, there are recognized future opportunities to perform additional analysis that could improve the understanding and be used to refine the preliminary work done and submitted under this memorandum. Some of the follow-on studies may include:

• Perform debris flow runout modeling under post-fire conditions where threat of impacts by sediment-laden floods is high. • Perform mudflow, hyperconcentrated flow and flood modeling using 2-dimentional models. • Installation of precipitation gages to better identify orographic and rain shadow effects on rainfall amounts. • Monitoring and calculating post-storm sediment volumes in debris basins to better understand runoff generated sediment amounts in response to specific storm duration and intensity.

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References

Larsen, I.J., MacDonald, L.H., Brown, E., Rough, D., Welsh, M.J., Pietraszek, J.H., Libohova, Z., Dios Benavides-Solorio, J., and Schaffrath, K., 2009, Causes of post-fire runoff and erosion: water repellency, cover, or soil sealing?: Soil Science Society of America Journal, v. 73, no. 4, p. 1393-1407. doi: 10.2136/sssaj2007.0432. CAL FIRE, 2018a, WERT report for Holy Fire (CA-RRU-100160): http://www.fire.ca.gov/communications/downloads/Watershed_reports/HolyFire_WERT- Final9-28-18.pdf CAL FIRE, 2018b, WERT report for Thomas Fire (CA-RRU-100160): http://cdfdata.fire.ca.gov/admin8327985/cdf/images/incidentfile1922_3383.pdf Cannon, S.H., Gartner, J.E., Wilson, R.C., Bowers, J.C., and Laber, J.L., 2008, Storm rainfall conditions for floods and debris flows from recently burned areas in southwestern Colorado and southern California: Geomorphology, v. 96, issue 3-4, p. 250-269. doi: 10.1016/j.geomorph.2007.03.019. Cannon, S.H., Boldt, E.M., Kean, J.W., Laber, J.L., and Staley, D.M., 2010, Relations between rainfall and postfire debris-flow and flood magnitudes for emergency-response planning, San Gabriel Mountains, southern California: U.S. Geological Survey, Open-File Report 2010- 1039, 21 p. JE Fuller, 2018, Coldwater Canyon Wash geomorphology study. Draft final report prepared for

Riverside County Flood Control and Water ConservationPreli minar y District. Part 1- Field Reconnaissance and Geomorphic Assessment; Part 2- Future Erosion and Equilibrium Assessment; Part 3- Recommended Management Measures: JE Fuller Hydrology and Geomorphology, Inc., Tempe, AZ. Lamb, M.P., Scheingross, J.S., Amidon, W.H., Swanson, E., and Limaye, A., 2011, A model for fire-induced sediment yield by dry ravel in steep landscapes: Journal of Geophysical Research: Earth Surface. 116, F03006, doi.org/10.1029/2010JF001878 Lancaster, J.T., Spittler, T.E., and Short, W.R., 2015, Alluvial Fan Flooding Hazards: An Engineering Geologic Approach to Preliminary Assessment. California Geological Survey Special Report 227. Sacramento, CA. 46 p.ftp://ftp.consrv.ca.gov/pub/dmg/pubs/sr/SR_227/CGS_SR227_Alluvial_Fan_Engineering_ Geologic_Approach_Final_July_2015.pdf Moody, J.A., Shakesby, R.A., Robichaud, P.R., Cannon, S.H., and Martin, D.A., 2013, Current research issues related to post-wildfire runoff and erosion processes: Earth-Science Reviews, 122, p. 10-37. Morton, D.M., and Miller, F.K., 2006, Geologic map of the San Bernardino and Santa Ana 30' x 60' quadrangles, California: U.S. Geological Survey Open-File Report 2006-1217, scale 1:100,000, 199 p.,http://pubs.usgs.gov/of/2006/1217 Staley, D.M., Negri, J.A., Kean, J.W., Cannon, S.H., Schmidt, K.M., Laber, J.L., 2013, Objective Definition of Rainfall intensity-duration thresholds for the initiation of post-fire debris flows in southern California: Landslides v. 10, p. 547-562.

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Staley, D.M., Negri, J.A., Kean, J.W., Laber, J.L., Tillery, A.C., Youberg, A.M., 2017, Prediction of spatially explicit rainfall intensity–duration thresholds for post-fire debris-flow generation in the western United States: Geomorphology, v. 278, p. 149-162. Nicita, E., and Halverson, E., 2018, Soil resource specialist report. Burned Area Emergency Response (BAER) Report—Holy Fire, Cleveland National Forest. Corona, CA. 17 p. USFS (United States Forest Service), 2018, Burned Area Report (2500-8) for the Holy Fire. Cleveland National Forest. San Diego, CA. 14 p. https://www.fs.usda.gov/Internet/FSE_DOCUMENTS/fseprd594859.pdf

Preli minar y

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Appendix A

Preli minar y

PLATE 1

CC-08

CC-07

CC-06 CC-05

CC-04

Inundation hazard not mapped CC-03 downstream due to the limited CC-01CC-02 watershed burn percentage and the presence of a debris basin

MC-01

SC-03

IC-07

SC-01 IC-06 IC-05

SC-02

IC-04 IC-02 IC-03 HC-11

ICN-02 ICN-04 IC-01 ICN-05 ICN-03

HC-10 HC-06 HC-07

HC-05

HC-04 HC-03

HC-02

HC-01

HC-08 PLATE 2

HC-09

RC-01

MVC-01

MVC-02

LC-02

LC-01 LC-03 LC-04

DC-05

DC-04 POTENTIAL POST-FIRE DEBRIS FLOW INUNDATION AREAS DC-02 DC-01

MAP EXPLANATION Hazard Areas Higher Energy Flows - Moderate to high depth and velocity capable of moving cobbles and boulders. Low Energy Flows - Low to moderate depth and velocity capable of moving mostly silt, sand and woody debris. Steep Slope Hazard Area (Including area within burn perimeter)

HC-01 Channel Constriction Location (Choke Point)

FEMA Special Flood Hazard Areas A; AE; AO

USGS Debris Flow Segment Probability Estimates* 0-20% 20-40% 40-60% 60-80% EC-01 80-100%

Holy Fire Perimeter Dated 20180817 0 0.25 0.5 1 Miles * Likelihood of a debris flow in response to the design rainstorm with a peak 15-minute rainfall intensity of 24mm/hr. µ INDEX MAP CC-08

CC-07

CC-06

CC-05

CC-04

Inundation hazard not mapped downstream due to the limited CC-03 CC-02 watershed burn percentage and CC-01 the presence of a debris basin

MC-01

SC-03

IC-07

SC-01

IC-06

IC-05

SC-02

IC-04

IC-02 IC-03 HC-11

ICN-01 ICN-02 ICN-04 ICN-03 IC-01 ICN-05

POTENTIAL POST-FIRE DEBRIS FLOW INUNDATION AREAS

HC-10

MAP EXPLANATION HC-06 HC-07 Hazard Areas Channel Constriction Table Higher Energy Flows - Moderate to high depth and velocity HC-05 capable of moving cobbles and boulders. Choke Point No. Latitude Longitude Choke Point No. Latitude Longitude HC-04 Low Energy Flows - Low to moderate depth and velocity CC-01 33.7545 -117.4959 IC-02 33.7350 -117.4482 CC-02 33.7547 -117.4940 IC-03 33.7349 -117.4476 capable of moving mostly silt, sand and woody debris. CC-03 33.7551 -117.4935 IC-04 33.7356 -117.4485 HC-03 Steep Slope Hazard Area (Including area within burn perimeter) CC-04 33.7567 -117.4929 IC-05 33.7391 -117.4478 CC-05 33.7636 -117.4864 IC-06 33.7400 -117.4477 HC-01 Channel Constriction Location (Choke Point) CC-06 33.7644 -117.4862 IC-07 33.7418 -117.4476 CC-07 33.7712 -117.4871 HC-01 33.7202 -117.4380 HC-02 FEMA Special Flood Hazard Areas CC-08 33.7833 -117.4885 HC-02 33.7219 -117.4379 MC-01 33.7491 -117.4775 HC-03 33.7240 -117.4374 A; AE; AO SC-01 33.7404 -117.4675 HC-04 33.7249 -117.4370 SC-02 33.7377 -117.4627 HC-05 33.7260 -117.4365 HC-01 USGS Debris Flow Segment Probability Estimates* SC-03 33.7429 -117.4584 HC-06 33.7276 -117.4361 0-20% ICN-01 33.7330 -117.4529 HC-07 33.7275 -117.4335 PLATE 2 ICN-02 33.7326 -117.4535 HC-08 33.7188 -117.4313 HC-08 20-40% ICN-03 33.7321 -117.4549 HC-09 33.7151 -117.4274 ICN-04 33.7322 -117.4559 HC-10 33.7285 -117.4096 40-60% ICN-05 33.7314 -117.4585 HC-11 33.7348 -117.4336 IC-01 33.7317 -117.4518 60-80% 80-100%

HC-09 Holy Fire Perimeter Dated 20180817 0 0.125 0.25 0.5 Miles * Likelihood of a debris flow in response to the design rainstorm with a peak 15-minute rainfall intensity of 24mm/hr. µ PLATE 1 HC-01

HC-08

HC-09 PLATE 1

RC-01

MVC-01

MVC-02

LC-02

LC-01 LC-03 LC-04

DC-05

DC-04

DC-02

DC-01

POTENTIAL POST-FIRE DEBRIS FLOW INUNDATION AREAS

MAP EXPLANATION Hazard Areas Channel Constriction Table Higher Energy Flows - Moderate to high depth and velocity capable of moving cobbles and boulders. Choke Point No. Latitude Longitude RC-01 33.6986 -117.4028 Low Energy Flows - Low to moderate depth and velocity MVC-01 33.6880 -117.4032 capable of moving mostly silt, sand and woody debris. MVC-02 33.6849 -117.3970 Steep Slope Hazard Area (Including area within burn perimeter) LC-01 33.6769 -117.4097 LC-02 33.6790 -117.4091 LC-03 33.6768 -117.3985 HC-01 Channel Constriction Location (Choke Point) LC-04 33.6769 -117.3898 DC-01 33.6712 -117.4045 FEMA Special Flood Hazard Areas DC-02 33.6722 -117.4043 A; AE; AO DC-04 33.6735 -117.4026 DC-05 33.6753 -117.4003 USGS Debris Flow Segment Probability Estimates* EC-01 33.6459 -117.4184 0-20% 20-40% 40-60% 60-80% 80-100%

Holy Fire Perimeter Dated 20180817

0 0.125 0.25 0.5 EC-01 Miles * Likelihood of a debris flow in response to the design rainstorm with a peak 15-minute rainfall intensity of 24mm/hr. µ PLATE 2 Appendix B Geomorphic Overview A series of large canyons descend from the northeast flank of the Santa Ana Mountains toward the developed areas between the mountain front and Temescal Wash. From northwest to southeast, the canyons significantly impacted by the Holy Fire include Coldwater, Mayhew, “Sycamore”, Indian and its main northern tributary, Cow, Horsethief, Bishop, Rice, McVicker, Leach and Dickey. Several smaller, unnamed canyons drain steeply to the valley floor west of Lake Elsinore. Total relief from the crest of the range to the mountain front in the larger canyons ranges from about 601 m (1,972 ft) at Leach Canyon up to 1157 m (3,797 ft) at Coldwater Canyon. Total relief for the smaller canyons west of Lake Elsinore ranges from about 318 m (1,044 ft) to 392 m (1,285 ft). The large canyons typically exhibit steep side canyon walls and headwalls with 63 to 86% of the slope areas having gradients exceeding 47%; the mean slope in these same canyons ranges from 53% to 66%, with Rice and Leach Canyons comprising the low end and Coldwater Canyon comprising the upper end of the noted slope gradients. However, the larger canyons also tend to be long and narrow with respect to relief, with relief ratios ranging from just 0.12 to 0.17 and trunk channel gradients above the mountain front ranging from 5.9% to 9.3%. Smaller tributary canyons such as Dickey and “Sycamore” have steeper trunk channel gradients of 11.4% and 11.8%, respectively. The short canyons west of Lake Elsinore are much steeper with relief ratios ranging up to 0.38.

The soils on the source area slopes were burned at moderate to high severity and dry ravel due to disaggregation of the shallow soils is widespread. In addition, the bedrock units are generally deeply weathered and locally overprinted by past landslide movement. Most of the canyons, except for Coldwater, contain extensive alluvial backfill. Hence, there is an abundance of loose, erodible sediment that can be entrained into debris flows during intense rain events. The bedrock in the source area varies from deeply weathered metamorphic and igneous rocks, to locally resistant outcrops primarily composed of granite. This weathered material provides a source for both fine-grained debris flow matrix material as well as larger cobbles and boulders. It is also notable that extensive stands of variably burned trees and shrubs remain in many of the source canyon drainages; debris flows can entrain this vegetationPreli minar y and clog downstream culverts and the floatable woody debris can overtop spillways.

Review of the historic aerial photographs, summarized in Appendix C revealed only localized evidence for active surficial landslide failures, hillside erosion, or depositional features diagnostic of historic debris flow processes over the last 60 years. This contrasts with the high potential for debris flow hazard modeled by the USGS for the Holy Fire burn area, and may reflect the lack of recent fires in the area as well as possible lack of intense rainfall events following past wildfires. Additional specific observations from the available aerial photographs are provided in Appendix C.

Outwash from the major canyons over time has formed a series of alluvial fan deposits descending from the mountain front of the Santa Ana Mountains to the valley fill associated with Temescal Wash to the northeast. Alluvial fans form progressively over time by divergent flow along distributary channels, forming a diagnostic “radial” fan-shaped landform. Distributary channels form by a process of avulsion where one channel becomes blocked by debris flow and flood deposition, bank failure or capture, and future flows are diverted into a new flow path. This phenomenon leads to complex and unpredictable flow patterns on fan surfaces that can extend far beyond established channels and associated hazard zones designated based on riverine flood modeling.

The alluvial fans deposited by the larger canyons below the burn area are the result of deposition by a combination of streamflow and debris flow processes (e.g. Lancaster et al., 2015). Flow processes may transition from debris flow to hyperconcentrated flow or streamflow within a single storm event as energy dissipates due to changes in gradient or loss on channel confinement. In locations where debris flow surge fronts come to rest and larger particles deposit, recessional flows tend to overtop and continue downstream as hyperconcentrated flows. Channel gradients on alluvial fan surfaces proximal to the canyon mouths range from 4.5 to 8.9% and distal fan surface gradients range from 2.2 to 4.8%. The proximal fan gradients fall within the range of composite and debris flow fan gradients, as described by Jackson et al. (1987). Several steep, boulder-laden fans B-1 emanating from short steep canyons west of Lake Elsinore were deposited dominantly by debris flow processes and are more appropriately termed debris fans. These past debris flows may have been initially generated by shallow landslide failures in the source area rather than surficial erosion. Observed debris fan gradients range from 17.6 to 22.9%.

Based on review of aerial photography and field observations, most of the alluvial and debris flow fans are geologically young and susceptible to deposition and erosion under the current climatic conditions. However, the historically active hydrographic fan apex is down gradient from the topographic fan apex in some cases, such as Horsethief Canyon. A few alluvial fan surfaces, particularly southeast of the young fan below Horsethief Canyon, appear elevated, deeply incised, and disconnected from the original source canyons, and therefore no longer active under the current climatic regime.

Large alluvial fans have accumulated at the mouths of Coldwater and Mayhew Canyons, which have been extensively mined for aggregate material, resulting in substantial modification to the natural drainage patterns. The depth of the quarry pits excavated in these fans attests to the great volume of deposition here over late Quaternary time. Just west of the mouth of Coldwater Canyon, there is an entrenched meander that directs flows eastward; however, the Glen Ivy Spa on the north, inner bank of the channel below the mountain front has experienced historic flooding. Southeast and east of the Glen Ivy Spa, a berm constructed of alluvial debris restricts the flow path across the fan to a single unlined channel that circumvents the northwest side of a quarry pit; historic aerial photographs indicate the dominant flow path across the fan prior to mining is now occupied by the quarry pit. The modified channel passes through a series of breached infiltration basins before reaching the culvert at Glen Ivy Road, and low water crossing at Temescal Canyon Road. In contrast, the drainage below Mayhew Canyon has been trained to flow through a large culvert and then into a lined channel that drains steeply into another quarry pit. Aerial imagery indicates the Mayhew fan previously drained northward until it coalesced into a northeast-draining channel adjacent to Temescal Canyon Road.

The “Sycamore” creek fan is complex and was extensively modified for agricultural use and then by recent grading for a new residential tract. Drainage below the mountain front is mostly captured into a concrete/grouted boulder channel that traverses the fan above the tract and drains through a box culvert below Towhee Lane. The historic, and current, active channel then bends northeast through a low gap before bending northward again and reaching a large culvert below Santiago Canyon Road.

The Indian Canyon wash is confined below the mountain front to a valley with inset alluvial surfaces, and a distinct alluvial fan is not developed until the lower end of the Glen Eden Sun Club. A geologically young, bouldery debris flow deposit was observed just below the mountain front adjacent to the lower Korean Church Grace Retreat Center facility, which attests to the debris flow potential in this canyon; the timing of this debris flow event could not be constrained with the available aerial photographs. Historic topography and aerial imagery indicates there were two primary inset channels in the lower floodplain between the mountain front and the fan. The western channel is currently the dominant active channel for typical seasonal flows. The eastern channel has been extensively modified and partially backfilled, and a portion of the Glen Eden Sun Club overlies this abandoned channel; gaps in the constructed berm up-gradient of the club may provide a path for flows during post-fire storm events. In addition, several low-water crossings with culverts within the Club property are potential sources of avulsion. Cobbles and boulders are well exposed along the active western channel within the Club property, attesting to past high energy flows in this area. However, the abundance of rocks exposed here may also reflect past channel modification and enhanced erosion of finer sediment due to removal of sediment at a small basin above the Sun Club, resulting in potential sediment-starved flows downstream of the basin.

A large, unnamed, northern tributary of Indian Canyon drains through the upper facilities of the Korean Church. The natural channel conditions have been extensively modified and constricted at several locations by culverts and fill encroachment. Aerial photos indicate that flows have historically avulsed through a low saddle along the Elsinore fault into a northern drainage path at B-2 choke point ICN-01. Future avulsions may occur along this section of the canyon during the storm event considered in this study.

Horsethief Canyon drains onto a large geologically young alluvial fan. Seasonal flows are currently confined to an active channel located near the western margin of the fan surface below the mountain front, but northeast-trending distributary channels were observed in aerial imagery on the east side of this channel. The current hydrographic fan apex manifests farther downstream above the Bosley Road Crossing; however, no evidence of a historic avulsion was observed at this location in the available aerial photographs. The WERT assessment and initial phase of field work for the current assessment identified the presence of several choke points at, and above, Bosley Road that could potentially result in avulsions during a large debris flow event. Channel constrictions included several culverts for road crossings and the confluence with Cow Canyon, which collects into a modified and possibly undersized channel downstream. Subsequent observations indicate that as of October 12, 2018, the crossings above Bosley Road have been removed and the crossing at Bosley Road has been replaced by a combination low-water crossing with CMPs; these improvements may reduce the potential for avulsions to occur. Another mitigating factor is the presence of a berm of rocky alluvial debris up to about 2 m high that was cleared from the upper portion of the fan to allow planting of a citrus orchard and piled along the east bank of the active channel. This berm limits potential avulsions to the northeast across the fan, except at a few low points for old dirt road crossings. Potential avulsions north of this berm were considered in the hazard mapping and resulting flows could potentially impact the Bosley Road culvert for constructed drainage along the west side of the Horsethief Canyon residential development, and residences to the northeast. The upper portion of this residential tract was built on older fan deposits; however, the lower portion of the tract impinges on the younger fan system north of Bosley Road.

Rice Canyon drains onto a broad, geologically young alluvial fan below the mountain front. Seasonal flows follow a distinct incised channel that bends northward along the northwest margin of the fan, where it is joined by the Bishop Canyon wash. Historic topographic surveys from 1940 and subsequent aerial imagery illustrate the same blue-line drainage path; however, geomorphic evidence suggest that flows have followed an abandoned channel near Lincoln Street on the southern margin of the fan in geologically recent times. The area northeast of the fan surface is underlain by incised older alluvial deposits. Evidence of geologically young debris flow deposits were observed above the mountain front in Rice Canyon during this assessment. A small residential tract is present southeast of the channel bend at the mouth of the canyon along Dale Court, and the Rice Canyon Elementary School is located below Lincoln Street to the east. Both in the WERT and this assessment, identified the potential for flows to avulse at the channel bend and potentially inundate the residences and school, and possibly more distant residences along Avocado Way. Subsequent observations during this assessment documented that the capacity of the berm above the residences had been enlarged and that a large, 3.5 to 4 m high berm was constructed of alluvial debris along the outer bank of the channel bend above the school. This berm was considered in this assessment and is expected to confine the storm flows considered for this study within this section of the channel. However, given the apparent lack of compaction effort and armoring, this berm should be considered as a temporary feature that will need inspection during and after storms. The north end of the active Rice Canyon wash drains into a complex system of quarry excavations, and given the topographic complexity, no attempt was made to map the potential distal inundation paths within this area.

McVicker Canyon drains southeastward and has deposited a large fan below the mountain front, which is now largely developed with residential tracts. A large, engineered debris basin was reportedly constructed above the mouth of the canyon in 1998 with an initial design capacity of 242,000 cy; the basin now reportedly has roughly 90% of this capacity. The flow path below the basin is now confined to a concrete-lined constructed channel. Historic aerial imagery and topography indicate that prior to modification, McVicker Canyon contained extensive, braided alluvial deposits that were embayed well above the topographic fan apex, and that there was not a well-defined, preferred channel path across the fan. Much of this thick alluvium was removed prior to, or during, construction of the dam, thereby increasing capacity. The basin capacity will likely B-3 contain potential debris flow deposits associated with assessed storm event. However, there is a low potential that cumulative debris and flood flows may exceed the basin capacity and floatable debris could pass through the spillway. Large floatable debris could potentially clog the downstream box channel where the channel narrows, or clog the box culvert at Grand Avenue.

A large debris basin was also constructed within Leach Canyon above the confluence with Dickey Canyon wash. The basin was reportedly constructed in 1955 with a design capacity of 140,000 cubic yards; however, recent RCFCWCD surveys indicated a reduced capacity of 90,000 cy. As October 12, 2018, removals were in progress to increase the basin capacity and a new debris rack consisting of 6 ft high, 8" diameter, cement-filled pipes spaced roughly 3 ft on center was installed above the spillway. Floods have reportedly filled the basin and flowed through the spillway in the past, and the new debris rack should reduce the potential for large woody debris to escape past the basin. Much of the alluvial fan area downstream of the basin has now been modified by residential development and for a grade-control structure above Grand Avenue, but the channel downstream of the basin is unlined.

Dickey Canyon is a southern tributary of Leach Canyon, but is relatively steep and has formed its own distinct alluvial fan. Historic imagery indicates the preferred flow path skirted the northwest margin of the fan as apparent from old topography. The current active channel is now farther to the southeast along the mapped USGS blue line, and confined to a concrete-lined, trapezoidal channel where it traverses the existing residential tract. The existing culverts for crossings at Toft Road and Brookstone Lane are undersized with respect to the HEC RAS modeling of the 100-year storm event. In addition, geologically young debris flow levee deposits were observed upstream of the development at channel bends; avulsions may occur at channel bends and modified channel banks.

Several relatively short, steep canyons drain toward the valley west of Lake Elsinore and south of Dickey Canyon. Debris fans containing large boulders, locally exceeding 2 m in diameter, are present along this section of the mountain front. Homes have been constructed on and below these debris fans. Review of aerial imagery did not identify evidence for historic debris fan activity in the last 60 years.

B-4 Appendix C

Preli minar y Holy Fire Inundation hazard Mapping Aerial Photo Review Date Frame Number Scale Source Location Comments

Fans not yet affected by quarries; Temescal Canyon and Glen Ivy Roads present, but not I‐15; active Mouth of Coldwater Canyon and Mayhew Canyon distributary channels just east of Choke Point CC‐04 and then bend and splay to northeast through 9/22/1953 AXM‐6K‐78 ≈1:20,000 USDA Fan north to Temescal Wash location of current huge quarry pit area. Primary active channel at Glen Ivy Road appears to be at same location as current; broad active channel area appear to intersect Temescal Canyon Rd from Glen Ivy intersection northwest to old structure (West channel on old RCFCD topo)

Lower Coldwater Canyon and Fan, and Mayhew Orchards and a few structures at mouth of Coldwater Canyon, with possible multiple channels or 9/22/1953 AXM‐6K‐79 ≈1:20,000 USDA Fan to Temescal Wash graded strips; Mayhew fan with multiple young‐looking distributary channels, with the dominant channel trending just west of chokde point MC‐01; local preliminary evidence of I‐15 grading Apex of Mayhew Canyon fan extends well above mountain front to first large confluence of tributaries; "Sycamore" Creek appears to drain primarily along its current path through the 9/22/1953 AXM‐6K‐80 ≈1:20,000 USDA Mayhew and "Sycamore" Canyons northeastern gap; the large concrete‐lined pool and ranch buildings at mouth are present (along Elsinore fault lineament); Indian Truck Trail is present

No development at Korean church facilities; active channel meandering near east margin of lower Mayhew Canyon and Indian Canyon/northern 9/22/1953 AXM‐6K‐81 ≈1:20,000 USDA facility; young flood plain within facility area; old active channel on northern tributary is mostly tributary east of confluence away from SE bank of floodplain (pushed against bank now); ICN‐01 and 05 are along strands of Elsinore fault; uppermost facility looks like a broad active channel area Upper Mayhew, Indian, Cow and Horsethief Vegetation in high country does not look impacted by recent fires; Apex of active deposition in 9/22/1953 AXM‐6K‐82 ≈1:20,000 USDA Canyons above Mountain front Indian Canyon extends up canyon to about 1,800 ft. Upper Indian and Horsethief Canyons, Trabuco 9/22/1953 AXM‐6K‐83 ≈1:20,000 USDA Peak and Upper Trabuco Canyon Area does not appear affected by fires Crest of Santa Ana Mountains and Trabuco Peak 9/22/1953 AXM‐6K‐84 ≈1:20,000 USDA near center Area does not appear affected by fires 9/22/1953 AXM‐6K‐85 ≈1:20,000 USDA Mainly upper Trabuco Canyon Area does not appear affected by fires Holy Fire Inundation hazard Mapping Aerial Photo Review Date Frame Number Scale Source Location Comments Lake Elsinore, east of burn area and mountain 1/28/1962 1‐169 1:24,000 RCFCD NA ‐ too far northeast; Lake appears dry front Lake Elsinore, east of burn area and mountain 1/28/1962 1‐170 1:24,000 RCFCD NA ‐ East of burn area and mountain front front Distributary channel fabric on upper geomorphic fan and apex of hydrologic fan are prominent; contact between young and old fan deposits east of active channel is also clear; much of the lower Horsethief development north of Bosley Road overprints the young hydrologic fan; distal fan and Horsethief Canyon, active and old fans to 1/30/1962 3‐448 1:24,000 RCFCD older encompassed fan above Temescal Canyon Rd has been cleared but still distinguishable; no Temescal Wash orchard yet on upper fan; junction with Cow Canyon appears undisturbed by man; much of older alluvial fan surface has been brushed, but original texture still visible; circular (empty) reservoir? at mountain front present; large channel SE of older fan deposits partially modified by quarries East of Photo 3‐448, including more quarries in foothill area; Large channel SE of older fan and NW of quarries is filled with alluvium below mountain front and drains in single channel to a fan at the north limit of Qof, and a second small distinct fan below old channel bank on southern meander of 1/30/1962 3‐449 1:24,000 RCFCD Horsethief to Rice Canyon and quarries to east Temescal Wash; much smaller channel to west only drains a small canyon in Qof ‐ The main drainage has now been trained to drain/outlet through the smaller west channel; Elsinore fault lineament at range front is prominent; Lower Rice Canyon wash partially modified by quarrying (see 3‐450) Well established active channel bends north at mouth of Rice Canyon as it does today ‐ channel path appears natural and unmodified except for small oblique training berm above mouth, but not currently against active channel; braided alluvial wash follows northwest margin of young fan 1/30/1962 3‐450 1:24,000 RCFCD Rice, Bishop, McVicker and Leach Canyons through gap in hills and widens before entering quarry area; small dam on eastern channel above quarries; active channel flow above mouth of Rice is primarily along southern margin of canyon; distal floodplain below Rice Canyon fan flows southeast along toe of McVicker fan; Sparse vegetation in Rice McVicker and Leach Canyons presumably from 1954 and 1956 fires

McVicker Canyon contains much more ponded alluvium in the channel upstream of mountain front than Rice; McVicker contains braided alluvium in canyon and lacks a distinctive primary incised channel below the mountain front, suggesting elevation of base level is not subsiding over time. McVicker and Leach Canyons and Elsinore Basin present at Leach Canyon, but little evidence of fresh sediment; alluvial fill extends upstream 1/30/1962 3‐451 1:24,000 RCFCD Mountain Front of basin to first sharp channel bend; geomorphic evidence for possible large old bedrock slide or debris fan on south side of canyon above dam; apparent incised older debris fan below dam sourced in canyon west of Dickey Canyon; active channel of Dickey canyon appears to be on NW side of its fan at mouth of canyon

Dormant debris fans apparent on steep slopes west of Lake Elsinore; no evidence of recent activity; only minor ground clearance along base of fans above Laguna Ave; no house in small northeast‐ 1/30/1962 3‐452 1:24,000 RCFCD Leach and Dickey Canyons, to El Cariso trending drainage between Dickey and Elsinore fans (VAR 73); Highway 74 and some improvements already present at El Cariso, but no evidence of recent channel scour Holy Fire Inundation hazard Mapping Aerial Photo Review Date Frame Number Scale Source Location Comments Shallow reservoir/lake on Temescal Wash just above confluence with Indian Canyon Wash, not in contact with small dam just downstream; "Sycamore" creek mostly incised with just a small fan Northwest to Southeast line ‐ Temescal Wash where it enters Temscal Wash; Indian Canyon wash fan apex at lower end of Glen Eden, with 6/27/1967 6134 ≈1:12,000 WRD and lower ends of "Sycamore", Indian, and meandering braided channel above; active channel primarily on west side of fan with two primary Horesthief Canyon washes smaller active distributary channels to east and young but inactive fan farther to SE; old dirt road crossing at choke point IC‐06; no fan on small incised channel to east

In lower reach of Horsethief Canyon wash, the wash splits into west and east branches around slightly elevated Qof surface, resulting in more restricted flow path; evidence for second fan apex Lower Indian and lower Horsethief Canyon 6/27/1967 6135 ≈1:12,000 WRD on western channel below constriction; structures present along wash above Temescal Canyon Rd washes and railroad tracks (GO‐231); Horsethief channel east of constriction (at GO‐233). Hydrologic apex above Bosley Road with distributary channels trending NE to HC‐07 from about HC‐05 Lower Horsethief Canyon wash and old fans to 6/27/1967 6136 ≈1:12,000 WRD Relatively minor alterations to geomorphology southeast HC‐10 between fans and quarries is on western of two active channels, which cuts through old Old fans east of lower Horsethief Canyon wash 6/27/1967 6137 ≈1:12,000 WRD terrace bank that parallels Temescal Wash channel; larger fan apex east of HC‐10 on eastern and quarries to east channel; quarries mostly in bedrock per geologic map (clay deposits?) Quarry area and lower portion of Rice Canyon Portions of broad, active lower flood plain valley of Rice Canyon still intact (not yet quarried), locally 6/27/1967 6138 ≈1:12,000 WRD Wash encompassing narrow ridge Main Rice Canyon wash channel bends north along northwest side of distinct broad, young fan; 6/27/1967 6139 ≈1:12,000 WRD Rice Canyon wash and fan Area northeast of fan is not Qya as shown on geologic map ‐ consists of highly dissected mixed rock units and Qoa east of mapped fault trend, part of southeast tributary of Temescal Wash Eastern margin of Rice Canyon fan and low hills to 6/27/1967 6140 ≈1:12,000 WRD Relatively minor alterations to geomorphology east Sparsely developed rural area; Qya continues southeast from fan and southwest of low hills of Qoa 6/27/1967 6141 ≈1:12,000 WRD Area east of Rice Canyon fan and mixed bedrock units bounded by faulting Holy Fire Inundation hazard Mapping Aerial Photo Review Area east of Rice Canyon fan, and west of Lake Sparsely developed rural area; Qya continues southeast from fan and southwest of low hills of Qoa 6/27/1967 6142 ≈1:12,000 WRD Elsinore and mixed bedrock units bounded by faulting; old Lake shorelines visible 6/27/1967 6143 ≈1:12,000 WRD Area north of northern corner of Lake Elsinore Sparsely developed rural area; old shorelines visible above northwest end of lake Most of McVicker fan surface appears young and unaltered with small distributary channels all New photo line SW of line 6134‐6143 (SE to NW) across surface with no primary incised channel; hydrologic apex appears to be up in canyon above 6/28/1967 6374 ≈1:12,000 WRD ‐ Much of McVicker Canyon fan and lower reach mountain front; fan impinges to south against active channel in lower reach of Leach Canyon wash of Leach Canyon wash in orchards Dark lineaments observed to trend down McVicker and Rice Canyon fans may be water bars? Portions of Rice Canyon fan overprinted by agriculture; Channel fabric on Rice fan appears young, McVicker fan, mouth of McVicker Canyon, and 6/28/1967 6375 ≈1:12,000 WRD but more irregular than McVicker; small fan present below canyon between Rice and McVicker; A southeast portion of Rice Canyon fan broad floodplain drains southeastward from the SE side of the Rice Canyon fan past the distal NE portion of the McVicker fan North bend of distinct active channel at mouth of Rice bends northward along northwest margin of fan, as it does today; fan surface young but no evidence of fresh activity (see description for Photo 6/28/1967 6376 ≈1:12,000 WRD Mouth of Rice Canyon and associated fan 6139); dirt road across mouth of Bishop Canyon to Bay Horse Ranch is present; Rice canyon wash widens downstream through low hills in area of current quarry facility Mouth of Rice Canyon, Bishop Canyon and Bay Portions of Bay Horse Ranch already cleared, with a modest‐size canyon to north; source areas 6/28/1967 6377 ≈1:12,000 WRD Horse Ranch mostly undisturbed by man Mountain front between Rice Canyon and Mountain front marked along main strand of Elsinore Fault; a series of relatively small canyons 6/28/1967 6378 ≈1:12,000 WRD Horsethief development area drains the lower portion of the range here. Circular reservoir at mountain front along Elsinore Fault lineament, with adjacent agriculture; 6/28/1967 6379 ≈1:12,000 WRD Mountain front southeast of Horsethief Canyon original drainage course below HC‐08 visible through ag on old fan surface. Many trees in Horsethief and Cow Canyons above confluence (at GO‐11 and GO‐12) Horsethief and Cow Canyons fairly confined above the confluence; subtle evidence past avulsions Mouth of Horsethief Canyon and fan below and flows across fan to northeast (prior to modification for orchard and association placement of 6/28/1967 6380 ≈1:12,000 WRD mountain front boulder pile along east bank of channel); however active hydrologic apex is north of mountain front above Bosley Road Channel pattern along Indian Canyon wash at lower Korean Church facility appears largely the same Horsethief Canyon to Indian Canyon along as in the 1953 photos; some brush clearance at and around the lower portion of the upper facility 6/28/1967 6381 ≈1:12,000 WRD Mountain front extending northwest along truck trail; eastern channel through future Glen Eden Club site is unmodified, but less prominent than the west channel Holy Fire Inundation hazard Mapping Aerial Photo Review Indian to "Sycamore" Canyon along mountain Sycamore fan drainage slightly modified across top of orchard at chokde point SC‐02 where 6/28/1967 6382 ≈1:12,000 WRD front transverse culvert is now located; concrete pool appears empty Mayhew forms prominent elongate, north‐trending fan with primary active channel slightly west of 6/28/1967 6383 ≈1:12,000 WRD Sycamore Canyon to mouth of Mayhew Canyon center, and small distributary to east; apparent vegetation change along old fan boundary in agricultural fields. Active drainage on upper portion of fan mostly confined to a wide channel near the center of the fan, just west of choke point MC‐01; no quarry pits yet; the channel becomes more distributary at a possible hydrologic fan apex near a cross road east of Maitri Road; distributary channel continues 6/28/1967 6384 ≈1:12,000 WRD Mayhew Canyon fan north to Temescal Canyon Road and elevated Qvof surface to north (small tertiary fans here), which confines and redirects flows to a broad, northeast‐draining canyon that drains to Temescal Wash (small distal fan at confluence?) All of Mayhew fan flows turn east at Temescal Canyon Road; no quarries at Coldwater fan yet; primary active channels on Coldwater fan similar to location in 1953; apparent distributary fan Mayhew Canyon fan to mouth of Coldwater 6/28/1967 6385 ≈1:12,000 WRD surface fades out above Glen Ivy Rd crossing; facility at Glen Ivy Spa appears a bit more distinct than Canyon in 1953; channel northeast of Temescal Canyon Rd at choke point CC‐06 is more prominent than in 1953 with recent deposition apparent 6/28/1967 6386 ≈1:12,000 WRD Coldwater Canyon fan Same notes as Photo 6385 New photo line SW of line 6374‐6386 (NW to SE) ‐Coldwater Canyon channel area is heavily wooded throughout as in 1953, hiding any sand or water 6/28/1967 6428 ≈1:12,000 WRD Coldwater Canyon flow Evidence of fresh channel flow and sandy deposition in Mayhew Canyon up to first major 6/28/1967 6429 ≈1:12,000 WRD Mayhew Canyon and drainages to northwest confluence, then channels above are more vegetated 6/28/1967 6430 ≈1:12,000 WRD Mayhew Canyon above mountain front Same notes as Photo 6429 "Sycamore" Canyon and northern Indian Canyon Extensive trees and shrubs in "Sycamore" Canyon channel and in Indian Canyon tributary channel 6/28/1967 6431 ≈1:12,000 WRD tributary along Mountain front near upper Korean Church facility; no evidence of recent fires Recently active wash deposits visible up to first major confluence; evidence of local surficial 6/28/1967 6432 ≈1:12,000 WRD Indian Canyon along mountain front instability/failures on steep slopes ascending from channel; no evidence of recent burns; Old alluvial surface remnants elevated well above active channel Alluvial fill accumulated in Cow Canyon with scattered trees; dense trees/shrubs in channel farther 6/28/1967 6433 ≈1:12,000 WRD Centered on Cow Canyon above mountain front up canyon Abundant trees/shrubs in lower channel area; Old alluvial surface remnants elevated well above 6/28/1967 6434 ≈1:12,000 WRD Horsethief Canyon above Mountain front active channel

Evidence of surficial instability on steeper slopes; vegetation not as dense as Horsthief, possibly a 6/28/1967 6435 ≈1:12,000 WRD Centered on Rice Canyon above Mountain Front vague reflection of the Jameson and Cornwell fires in the are during 1954 and 1956, respectively Holy Fire Inundation hazard Mapping Aerial Photo Review McVicker Canyon much straighter than Rice, and braided alluvial backfill extends much farther up 6/28/1967 6436 ≈1:12,000 WRD Rice and McVicker Canyons above Mountain front canyon; vegetation not as dense as Horsthief, possibly a vague reflection of the Jameson and Cornwell fires in the are during 1954 and 1956, respectively Leach Canyon debris basin present (built in 1955) and appears to contain some fresh sandy debris approaching spillway, but not distinct in channel below dam; relatively sparse vegetation is likely 6/28/1967 6437 ≈1:12,000 WRD McVicker Canyon and lower Leach Canyon remnant from 1954 Jameson fire; unusual east‐west vegetation lineaments and some channel score on slopes south of Leach Canyon; no houses or Amorose St. below dam yet

See previous Leach Canyon notes for Photo 6437; vegetation lineaments prominent recovering man‐ made alteration?; orchards below future Grand Ave alignment; active channel below Leach Canyon follows south bank of valley below dam and then migrates to central portion of fan, beginning wll 6/28/1967 6438 ≈1:12,000 WRD Leach Canyon and lower Dickey Canyon above Grand Ave; it appears the most active channel below the mouth of Dickey Canyon used to follow the topographic channel northwest of the current blueline constructed channel on northwest margin of debris fan, through current home locations Fans below Grand Avenue modified for orchards; common trees/shrubs above mountain front in Dickey Canyon; old road/trail up ridge east of Dickey Canyon to crest; most of roads below debris Lower Dickey Canyon and northwest portion of 6/28/1967 6439 ≈1:12,000 WRD fans and southwest of Laguna Ave now graded but only a few homes; boulder‐strewn area of fans debris fans west of Lake Elsinore prominent, but not obviously recently active; fresh cut slope northwest of Mandaville Way at end of cleared area Fresh grading northwest of Dreycott Way but no houses yet; only one small structure below 6/28/1967 6440 ≈1:12,000 WRD Debris fans west of Lake Elsinore Lakeview Ave at prominent southeastern debris fan between Riverside Drive and Dreycott Way; no evidence of recent activity of debris fans Note: Photo source is WRD not WRC; WRD may be Water Replenishment District of Southern California Holy Fire Inundation hazard Mapping Aerial Photo Review Date Frame Number Scale Source Location Comments Mouth of drainage between old Horsethief fan and quarries shows evidence of fresh sandy Centered north of Temescal Wash near Alberhill deposition, presumably from 1969 winter storms; deposition on fans is most prominent at mouth of 11/22/1969 22 1:12,000 RCFCD quarry facilities smaller western channel with an avulsion back into the main eastern channel (see notes for 1967 Photo 6137 and 1962 Photo 3‐449) Centered north of Temescal Wash northwest of More exposure of drainage described in photo 22; Small fresh sandy fans emanating from small 11/22/1969 23 1:12,000 RCFCD Alberhill quarry facilities canyons in Qof to west Centered at Temescal Wash at base of older Long drainage from mountain front across older fan; 1969 flood flows may have crossed Temescal 11/22/1969 24 1:12,000 RCFCD Horsethief fans Canyon Rd based on fresh sandy deposits north of road Fresh flows appear to have been contained in the main western channel, with no significant Lower Horsethief Canyon wash down to Temescal avulsions to northeast at hydrologic apex above Bosley Road. Flow area widened above Temescal 11/22/1969 25 1:12,000 RCFCD Wash Canyon Rd, possibly inundating some facilities, and likely flowing over Temescal Canyon Rd; Large sandy deposit all the way across Temescal Wash

Same notes as above for Horsethief Canyon; smaller drainage between Horsethief and Indian shows evidence of fresh scour and sandy deposition, including VAR 35 and possibly VAR 34; also evidence of fresh deposition on fan extending down to VAR 36 south of Bosley Road. No Korean Church facilities in Indian Canyon or northern tributary; Indian Canyon Wash only shows modest evidence Lower Horsethief Canyon wash westward to of fresh flows above Glen Eden Club, but some activity along eastern channel. Evidence of scour and 11/22/1969 26 1:12,000 RCFCD lower Indian Canyon wash sandy deposition along lower northern tributary, including north of current channel, and in part flowing north around knob at Elsinore fault; Small facility at Glen Eden appears unaffected, but evidence of fresh flows become more distributary on fan north of facility and appear to have backed up against railroad alignment; no substantial evidence of fresh scour/deposition in nearby smaller canyons

Same notes as above for Indian Canyon; evidence for fresh scour/sandy deposition on Sycamore 11/22/1969 27 1:12,000 RCFCD Lower Indian Canyon to "Sycamore" Canyon fan, diverted around orchard at location of current transverse drain, and flow along current channel to north; large concrete pool appears empty; second open reservoir at mouth of next canyon to NW Same notes as above for "Sycamore" Canyon; Fresh scour and sandy deposition across width of Mayhew Canyon above mouth; fresh scour/sandy deposition on fan mostly contained in broad, 11/22/1969 28 1:12,000 RCFCD "Sycamore Canyon" to mouth of Mayhew Canyon central channel, with one possible small avulsion to northeast; fan appears geologically young and mostly undisturbed by man, but bounded by orchards to east; no significant fresh scour or deposition noted in smaller canyon channels Same notes as above for Mayhew Canyon; evidence of fresh scour/deposition mostly observed Last photo of this line ‐ Mouth and lower portion 11/22/1969 29 1:12,000 RCFCD below first major confluence, with local evidence of fresh channel activity through trees farther up; of Mayhew Canyon only minor evidence of fresh surficial failures on slopes 11/22/1969 30 1:12,000 RCFCD Northeast of Temescal Wash NA 11/22/1969 31 1:12,000 RCFCD Mostly northeast of Temescal Wash NA 11/22/1969 32 1:12,000 RCFCD Temescal Wash and quarries to southwestNA Temescal Wash and quarries to southwest to 11/22/1969 33 1:12,000 RCFCD Small dam on east distributary channel of Rice Canyon wash, upstream of large quarry pit mouth of Rice Canyon wash Holy Fire Inundation hazard Mapping Aerial Photo Review

Same notes for Rice Canyon wash as above; Farther south, fresh scour/sandy deposition appears to have followed two channels, one on either side of the broad Rice Canyon wash; flow was more substantial in the eastern channel, but was largely diverted to the west side of the wash at an 11/22/1969 34 1:12,000 RCFCD Quarry pits at mouth of Rice Canyon Wash upper quarry operation; the combined flow then continued to the north and dumped into another pit, where a sandy fan was deposited; fresh scour/sandy deposition also observed from smaller canyon to west, sourced from low part of range northeast of Bishop Canyon Same notes as above for lower Rice Canyon wash; see notes for 1962 photo 3‐449; extensive fresh Alberhill Quarry pits from Lower Rice Canyon scour and sandy deposition in channel between quarries and Qof deposits; active channel pushed 11/22/1969 35 1:12,000 RCFCD wash to east portion of lower Horsethief Qof against west bank of wash, and then drains into small western fan (see notes for photos 22 and 23 deposits above) Much of fan is covered with orchards; circular reservoir present at mountain front; long channel Older fan (Qof deposits) northeast of Horsethief 11/22/1969 36 1:12,000 RCFCD across fan starting at choke point HC‐08 (top of VAR 63) shows evidence of fresh scour and sandy canyon and west of Alberhill quarries deposition Evidence of significant scour and sandy deposition along both Horsethief and lower Cow Canyon washes; orchard not yet present on fan above Bosley Road, east of channel; flows do not appear to Horsethief Canyon along mountain front and have avulsed beyond eastern channel bank either at geomorphic fan apex or lower hydrologic apex 11/22/1969 37 1:12,000 RCFCD upper fan above Bosley Road, although there is evidence for a short avulsion over the west bank; Evidence of clearance along a narrow swath paralleling the east bank, but does not appear to be the existing rock pile, which was reportedly derived from clearance of the orchard field to the east

Same notes as above for Horsethief and Cow Canyons; evidence of fresh flows in Cow Canyon and Horsethief Canyon to Indian Canyon along from two tributaries to Horsethief Canyon above the mountain front; Evidence of fresh scour and 11/22/1969 38 1:12,000 RCFCD mountain front sandy deposition from two fan sources above Bosley Road west of Horsethief, and in channel east of Indian Canyon ‐ see description of Photo 26 above See notes for Photo 26 above; little evidence of significant surficial failures or landslides in source Last photo of this line ‐ Indian Canyon and part 11/22/1969 39 1:12,000 RCFCD areas of Indian Canyon; Debris flow lobe noted in field adjacent to lower Korean Church facility not of northern tributary along mountain front obvious 11/22/1969 40 1:12,000 RCFCD Northeast of Temescal Wash NA 11/22/1969 41 1:12,000 RCFCD Temescal Wash NA Temescal Wash and quarry area to southwest, 11/22/1969 42 1:12,000 RCFCD NA north of Lake Elsinore Quarry area and low hills east of Rice Canyon 11/22/1969 43 1:12,000 RCFCD NA wash and east edge of fan Evidence of fresh scour and sand deposition along channel on north bank of Rice Canyon at mouth, bending north and flowing into quarry areas to north (see notes for Photos 33 and 34 above); no 11/22/1969 44 1:12,000 RCFCD Rice Canyon wash and fan evidence of avulsion onto other portions of Rice Canyon fan; fan is partially undisturbed by man, and partially utilized for agriculture; no homes below mouth of canyon; old berm just above mouth not a factor in flow path due to channel meander up stream

See notes above for Rice Canyon; Evidence of local fresh scour/deposition just above mouth of Bishop Canyon, but absent or hidden by trees farther up; much fresh grading/clearance on Bay Rice Canyon wash and fan, Lower Bishop Canyon Horse Ranch plateau; evidence of fresh sandy deposition on small fan surface below VAR 33; 11/22/1969 45 1:12,000 RCFCD and Bay Horse Ranch area to NW uncertain evidence of fresh flows at mouth of small canyon at VAR 32; evidence of fresh scour and possible debris cleanup on distinct fan below larger draw south of VAR 32; little evidence for fresh surficial failures or landslides on source area slopes Mouth of Rice Canyon northwest along mountain See notes above regarding Bay Horse Ranch area; no evidence of significant fresh surficial failures 11/22/1969 46 1:12,000 RCFCD front or landslides on source area slopes Mountain front area above Elsinore Fault Evidence of fresh surficial instability generally absent on slopes in source canyon areas, except at 11/22/1969 47 1:12,000 RCFCD between Rice and Horsethief Canyons local badlands topo along southeast side of Elsinore Fault Holy Fire Inundation hazard Mapping Aerial Photo Review Date Frame Number Scale Source Location Comments Northeast range front of Santa Ana Mountains 5/24/1974 435 1:24,000 RCFCD and Temescal Valley north of mouth of NA Coldwater Canyon (Flight W to E) Fan at mouth of Coldwater Canyon still mostly natural, with most active flow area forming a broad distributary channel system near the center of the fan (current location of quarry); distal channel crosses Glen Ivy Road near current location; appears to be two flow paths where it crosses Temescal Valley north of mouth of Coldwater 5/24/1974 436 1:24,000 RCFCD Temescal Canyon Road (as shown on old RCFCD 4 ft topo); evidence of Canyon wide recently active channel at location of Tom's Farms bridge, but channel appears less incised than current conditions; distributary channels on lower end of Mayhew Fan converge into recently active, ENE‐ trending channel along bluff to north and flows to Temescal Creek 5/24/1974 437 1:24,000 RCFCD Temescal Wash Same comments as for Photo 436 above Same comments as for Photo 436 above; Coldwater Canyon channel heavily vegetated above mountain front; little evidence for fresh surficial New Photo line south of 435 to 437 (Flight W to failures on source slopes overall, except possibly on steep SE‐facing slopes 6/20/1974 506 1:24,000 RCFCD E) ‐ Mountain front at Coldwater and Mayhew in upper Coldwater Canyon; Mayhew Canyon conditions similar to 1969 Canyons conditions, except there is now a small quarry operation on the eastern portion of the fan, east of the active channel area; portions of the fan northeast of the quarry have been modified for agriculture

Same comments for Mayhew fan as Photos 436 and 506 above; most of "Sycamore" fan is modified for agriculture; active channel skirts east side of fields and follows present northern course through gap to northeast; Lower Coldwater Canyon to "Sycamore" Canyon Indian Canyon shows modification for small facility at Glen Eden and 6/20/1974 507 1:24,000 RCFCD fan and lower Indian Canyon wash subdued evidence of active flow paths from 1969 photos; no evidence of fresh flows on northeast portion of fan north of Glen Eden; Indian wash drains into unusual meander below small dam in Temescal Wash, which is entrenched into bedrock on northeast side of canyon

See notes above for Photo 507 for Indian Canyon wash; active wash "Sycamore" fan east to mouths of Indian and 6/20/1974 508 1:24,000 RCFCD deposits for Horsethief similar to path noted in 1969 photos, but deposits Horsethief Canyons along Temescal Wash in wash somewhat modified by subsequent flows in Temescal Wash

Young geomorphic fan mostly undisturbed and fan below hydrologic apex near Bosley Road is only locally overprinted by agriculture; no evidence of Indian Canyon wash eastward to Horsethief fans recent activity on fans; evidence of fresh flows in 1969 photos starting to 6/20/1974 509 1:24,000 RCFCD and Aberhill Quarries fade; see previous notes for 1969 Photo 25; west side of fan, west of active channel northwest of Aberhill quarries has been graded/cleared; no orchard on fan east of Horsethief Canyon wash Holy Fire Inundation hazard Mapping Aerial Photo Review Aberhill quarries and areas north of Temescal 6/20/1974 510 1:24,000 RCFCD NA Wash Evidence of fresh scour/deposition in channel throughout much of upper Horsethief canyon visible above trees; in contrast, much less evidence of New photo line south of 506 to 510 (Flight W to fresh scour or deposition in upper channels of Rice and McVicker Canyon; 6/20/1974 577 1:24,000 RCFCD E) ‐ Horsethief Canyon almost to crest and upper no evidence of significant fresh surficial failures, rilling or landslides on Rice and partial McVicker Canyons source slopes; McVicker with much more ponded alluvium into upper reaches of main canyon, with little sinuosity

See previous notes for Horsethief; Rice channel unchanged since 1969, except for more quarry disturbance in lower reaches of wash and much of Horsethief, Rice and McVicker Canyons, and east half of fan is overprinted by agriculture; McVicker shows small quarry 6/20/1974 578 1:24,000 RCFCD lower part of Leach Canyon along mountain front area in alluvium at mouth of canyon; agricultural modification on outer margins of McVicker fan; No fresh debris apparent behind Leach Canyon dam; no evidence of fresh surficial failures or landslides on source slopes

Rice Canyon fan ends to east‐northeast along older incised alluvium (along Mouth and fans of Rice and McVicker Canyons 6/20/1974 579 1:24,000 RCFCD fault zone); active flows follow northwest margin of fan toward quarries and Alberhill quarries and young fan flows head southeast to merge with distal McVicker fan 6/20/1974 580 1:24,000 RCFCD Area north of Lake Elsinore NA East‐west striped lineaments on slopes south of Leach canyon still visible; most of lower Leach and Dickey canyons fans occupied by agriculture; new New photo line south of 577 to 580 (Flight W to tract of homes on parcel northwest of Dreycott Way and southwest of 6/20/1974 648 1:24,000 RCFCD E) ‐ Leach Canyon down El Cariso and slopes west Laguna Avenue along mountain front; debris fans in this area appear of Lake Elsinore dormant; no significant evidence of fresh surficial failures or landslides on source slope areas; no evidence of significant fresh scour or deposition along channel in El Cariso area Mouth of Leach Canyon and mountain front 6/20/1974 649 1:24,000 RCFCD Same as 648 eastward to Lake Elsinore 6/20/1974 650 1:24,000 RCFCD Lake Elsinore NA Holy Fire Inundation hazard Mapping Aerial Photo Review Date Frame Number Scale Source Location Comments Two large aggregate pits and several smaller excavations now present on eastern portion of Coldwater fan, but drainage pattern on fan to west still roughly the same, with a possible training channel added; upper Mayhew West to east line ‐ Coldwater, Mayhew, fan and primary channel also substantially modified; Main channel now 4/14/1980 539 1:24,000 RCFCD "Sycamore", and portion of upper Indian Canyons trained over to east side of lower northern portion of fan, with an incised thalweg, to avoid extensive aggregate mining of lower fan; I‐15 alignment is now present; Sycamore appears unchanged since 1974; no fresh scars or erosion in source areas

See notes above; lower Indian Canyon has been trained above I‐5 to direct drainage below bridges; Additional Glen Eden Club facilities on west side Mayhew, "Sycamore" and Indian Canyons to 4/14/1980 540 1:24,000 RCFCD of wash since 1974, with modest redirect of channel?; eastern channel still Temescal Wash largely intact; Still no Korean Church facilities; much fresh grading/clearing along mountain front between Indian and Horsethief Canyons

See notes above; Horsethief channel generally unchanged, except trained above I‐15 to direct flows under bridges; modification of property north of "Sycamore" Canyon to Horsethief Qof fans and 4/14/1980 541 1:24,000 RCFCD Bosley Road on east side of channel; no orchard or rock pile east of Temescal Wash channel south of Bosley Road; active channels apparent but not as prominent as in 1969 following storms that winter

Drainage between Qof and quarries to east still trained against northwest bank into small western channel, which has a graded area to west; most of 4/14/1980 542 1:24,000 RCFCD Horsthief Wash and fans, and Alberhill quarries lower Rice Canyon wash is now overprinted by quarries, except for one section below two small dams; I‐15 looks essentially done with surfacing and bridges, but no cars apparent, so may be just before completion Alberhill quarries and areas north of Temescal 4/14/1980 543 1:24,000 RCFCD NA Wash 4/14/1980 544 1:24,000 RCFCD Area mostly north and east of Temescal Wash NA New west to east line of photos south of 539‐ 4/15/1980 610 1:24,000 RCFCD 544 ‐ Crest of Santa Ana Mountains near upper No evidence of recent burns or fresh surficial failures or landslides Indian Canyon Holy Fire Inundation hazard Mapping Aerial Photo Review Upper Horsethief to McVicker Canyons above No evidence of recent burns or fresh surficial failures or landslides; no 4/15/1980 611 1:24,000 RCFCD mountain front orchard at mouth of Horsethief See notes for photos 542 and 611; mouth of Rice Canyon still undeveloped Horsethief south to McVicker and partial Leach except for dirt road to mouth, with drainage pattern similar to 1969; 4/15/1980 612 1:24,000 RCFCD Canyons, Horsethief Qof and portion of Alberhill quarry operation across mouth of McVicker Canyon, but no basin yet; quarries near lower Rice Canyon wash some ground disturbance behind Leach Canyon debris basin dam; but no clear evidence of fresh ponded sediment

See notes for photo 612; Well established haul road from quarry at mouth of McVicker northward across Rice Canyon fan to quarry facilities in lower Rice Canyon wash; evidence of old water bars perpendicular to mountain 4/15/1980 613 1:24,000 RCFCD Horsethief fan south to Rice and McVicker fans front down McVicker fan; eastern 2/3 of Rice Canyon fan and portions of lower McVicker fan overprinted by agriculture; evidence of recent flows down Leach Canyon wash channel below dam, but unclear if it overtopped basin dam or derived from canyon southeast of dam Quarries in lower Rice Canyon; Rice, McVicker 4/15/1980 614 1:24,000 RCFCD and Leach Canyon fans and area north of Lake See notes for photos 612 and 613; Lake Elsinore appears full Elsinore 4/15/1980 615 1:24,000 RCFCD Area north and northeast of Lake Elsinore Highway 15 under construction No evidence of fresh scour, flooding or deposition in channel through El Cariso, and no evidence of significant fresh surficial failures or active New west to east line of photos south of 610 to 5/4/1980 679 1:24,000 RCFCD landslides in source area canyons above El Cariso; Same lack of active 615 ‐ McVicker Canyon south to El Cariso surficial failures or landslides in source areas of McVicker, Leach and Dickey Canyons Many houses now present at base of mountains just below, and locally on debris fans west of Lake Elsinore; no evidence of recent debris fan activity; McVicker Canyon south to El Cariso, including still no residential development on fan below Dickey Canyon, or below 5/4/1980 680 1:24,000 RCFCD mountain front and plain west of Lake Elsinore dam in Leach Canyon; some evidence of recent scour/deposition along channel in small canyon SE of Dickey Canyon and NW of Elsinore fans (at VAR 73 polygon) Mouth of McVicker Canyon southeast to Lake 5/4/1980 681 1:24,000 RCFCD See notes above Elsinore Holy Fire Inundation hazard Mapping Aerial Photo Review Date Frame Number Scale Source Location Comments Line north to south ‐ Mostly Temescal Wash and Lower "Sycamore" modified by onramps for I‐15, but otherwise similar as 7/27/1980 1079‐200 ≈1:30,000 USDA to northeast, north of "Sycamore" Canyon and before; Mayhew quarries west of ag areas east from margin of Mayhew Fan

7/27/1980 1079‐201 ≈1:30,000 USDA "Sycamore", Indian and lower Horsethief Canyons See notes for 1980 RCFCD Photos 540 and 541 Indian and Horsethief Canyons east to Alberhill 7/27/1980 1079‐202 ≈1:30,000 USDA See notes for 1980 RCFCD Photo 542 quarries Horsethief, Rice and McVicker Canyons, mostly 7/27/1980 1079‐203 ≈1:30,000 USDA See notes for 1980 RCFCD Photo 611 above mountain front Note: photos are small scale and less detailed than 1980 RCFCD photos