Plant seedling establishment often relies on facilitation from nearby plants, rocks, and other microsite characteristics, e.g. at a 1-meter scale. Favorable microsites may moderate temperature, increase available water, provide shade, and reduce herbivory, facilitating the risky transition from germination to establishment. Microsite characteristics vary considerably across the mesoscale. Establishment patterns of plants therefore often have strong spatial patterning related to microsite conditions. In arid environments, risks are especially pronounced. The giant saguaro cactus (Carnegiea gigantea) is an example of a long-lived arid land species occurring in remarkable heterogeneity of habitat conditions that facilitate establishment. The goal of this study is to investigate microsite patterns of saguaro establishment, important for saguaro conservation and restoration. On Tumamoc Hill (O’odham: Cemamagĭ Doʼag, “regal horned lizard”), long-term saguaro survey data of 5000 individuals has been collected since 1964. Previous research on Tumamoc Hill has shown that demographic patterns reflect slope aspect at the mesoscale. We are further investigating a smaller spatial scale, comparing random microsite features with establishment sites of saguaros, to better understand the variables that relate to the spatial pattern of saguaro establishment. We collected records of the species of associated vegetation, estimates of percent total vegetation cover, percent rock cover, percent non-native grass cover (buffelgrass), slope, aspect, elevation, and terrain ruggedness data for 30 randomly placed 1 meter diameter microsites within each of three subplots in each plot. We collected identical microsite variables where saguaros occur. Principal component analysis, generalized linear mixed models and other approaches are being used to detect contrasts between random microsite characteristics and those where saguaros have established, if any. We expect that patterns of saguaro establishment will be related to microsite characteristics and that establishment microsites will vary significantly from random sites. We further expect that these establishment patterns will help illuminate saguaro ecology, conservation, and restoration, and perhaps clarify why this important species occurs in such a wide variety of habitats across its range.