The State of New Mexico assumes no liability for the contents of this report or use thereof. The contents of this report reflect the views of the authors who are solely responsible for the facts and accuracy of the material presented. The contents do not necessarily reflect the official views of the State of New Mexico or the Department of Homeland Security and Emergency Management. The State of New Mexico does not endorse products or software. Use of particular products herein was solely for the purpose of completing this project. Trademarks or manufacturers' names appear herein only where and because they are considered essential to the object of this document. The report does not constitute a standard or specification. This report and accompanying maps are not substitutes for detailed, location specific geotechnical or geohazards analyses.

We present the method used and the resulting 1:750,000 scale map of collapsible soil susceptibility for New Mexico, the first time such a map has been generated in the western United States. Collapsible, or hydrocompactive soils are sedimentary deposits that under combined wetting and loading will subside significantly (up to 30% strains). Composed of water-sensitive-clay-rich sediments, these deposits present a common but difficult to map hazard across the desert Southwest, including New Mexico. However, because compaction of collapsible soils usually happens after structures have been built on them, their incidents are not well reported nor are they readily apparent from surface morphology. Maps of hydrocompaction susceptibility generally are done at scales greater than 1:24,000, allowing for detailed geotechnical sampling to take place combined with geologic mapping. This was not tenable at the scale of New Mexico. To overcome the lack of observable morphology, the paucity of reported incidents and the lack of statewide geotechnical data, we compiled a map of known but geotechnically-unconfirmed locales and then developed a multi-proxy-based spatially weighted average (i.e., an overlay method) of susceptibilities. Proxies used in this study are surficial deposit maps of depositional style, age, geomorphic setting, sediment provenance, and deposit texture; NRCS gSSURGO maps of both soil texture of the bottom 1/3 of the pedon, and the soil taxonomic classification to the great group level; a Köppen-Geiger climate zone map; NLCD land-use maps; and reported static water levels from the NMOSE Water Rights Reporting System. Not all proxies are available throughout the state, meaning that the number of proxies available at a location affected the reliability of the estimated susceptibility. Each proxy was iteratively assigned a weight, or quality factor, and a range of susceptibilities between zero (not susceptible) and four (extremely susceptible) depending on the proxy value. We assessed the effectiveness of each proxy by comparing the frequency of occurrence in and within 500-m of mapped hydrocompactive locales; at this point, we iterated on both the proxy quality and proxy susceptibility. Then, 500-m resolution rasters of quality-weighted susceptibility (total susceptibilities), average quality and the number of proxies used were generated. Breaks in raw total susceptibilities were assessed by examination of the histograms in and near (within 500-m) mapped hydrocompactive soils: < 0.5 was not susceptible, 0.5-1.5 was low susceptibility, 1.5 to 2.5 was moderate susceptibility, 2.5 to 3 was highly susceptibility, and > 3 was extremely susceptible. The new 500-m resolution, 1:750,000 scale maps of total hydrocompaction susceptibility, average quality of estimated susceptibility, and number of proxies used should be used together as a planning aid to assess the susceptibility of a region to hydrocompactive soils. They are not, however, substitutes for detailed, location specific geotechnical or geohazards analyses.

We present two 1:750,000 maps that provide a first-order approximation of rockfall susceptibility for the state of New Mexico. The maps are intended for regional planning purposes and determining where detailed studies may be warranted. 'Susceptibility' describes the natural propensity (likelihood) of the landscape to produce rockfall given adequate driving forces. An essential input for these maps was a preexisting, statewide map of rockfalls produced by Cardinali et al. (1990) using aerial photography. This map has a bias towards larger rockfalls and captures only a fraction of the total rock falls in the state, but nonetheless it is assumed to be a statistically valid subsample of the total. The first susceptibility map shows the point densities of the mapped rockfalls of Cardinali et al. (1990), which are contoured using the kernel function. It may serve as a proxy for where large rockfall events may occur in the future.The second rockfall susceptibility map relates mapped rock falls to nearby slope values. Using a 28 m DEM in ARC GIS, a slope map is created. We capture the maximum slope around a mapped rock fall point using a 300 m-radius window, which corresponds to the median of the error range in the mapped rockfall points. The average and maximum value of the slope within this window was obtained, but the frequency distribution curve for the average value is heavily skewed to low values, probably because most of New Mexico is relatively flat and spatial errors would result in a rockfall being on low-sloping ground. However, the maximum value within the window gave a quasi-normal distribution centered on a mean value of 29°a nd having a standard deviation of 12°. We chose to use these maximum values within the 300 m-radius window, with the assumption that most rock falls tend to accumulate on relatively steep talus slopes.Using the mean and standard deviations calculated from the distribution of these maximum slopes, we categorize the aforementioned slope map into three susceptibility classes. "Likely susceptible" zones correspond to slopes lying at or above the mean-less-one standard-deviation (17°). Locally in this zone are rockfall-generating ledges and steep slopes allowing rockfall transport. "Potentially susceptible" zones correspond to slopes in the range of 8-17°, bracketed by the mean-less-one standard-deviation and the 5th percentile of the aforementioned maximum slope frequency distribution. This zone may have small rockfall-producing ledges; it also includes a 470 m-wide buffer extending downslope (on 5-17° slopes) of Likely susceptibility areas, designed to capture rockfalls having sufficient momentum to travel notably downhill of ≥17° slopes. The 470 m value corresponds to the 90th percentile (excluding outliers) of mapped rockfall distances from the Likely susceptible zone. "Unlikely susceptible" zones include very low slopes (<8°) lying outside of the aforementioned buffer. Final processing steps involved down-sampling to 500 m grid-size consistent with a 1:750,000 final map scale.

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Mason, Mitigation Specialist. The Earth Data Analysis Center (EDAC) of the University of New Mexico digitized scans of rockfall maps for this project. The U.S. Army Corps of Engineers provided the high-resolution digital terrain model that served as a basis for all topographic data used in this investigation. ESRI provided the GIS software and tools used in processing spatial data throughout this project. DISCLAIMERThe State of New Mexico assumes no liability of the contents of this report or use thereof.The contents of this report reflect the views of the authors who are solely responsible for the facts and accuracy of the material presented. The contents do not necessarily reflect the official views of the State of New Mexico or the Department of Homeland Security and Emergency Management.The State of New Mexico does not endorse products or software. Use of particular products herein was solely for the purpose of completing this project. Trademarks or manufacturers' names appear herein only where and because they are considered essential to the object of this document. This report does not constitute a standard or specification. This report and accompanying map are not substitutes for detailed, location-specific geotechnical or geohazards analyses.