**1. Introduction**

Hurricane Odile was one of the most destructive storms to strike the Mexican state of Baja California Sur in terms of infrastructure damage [1]. It made landfall just after midnight on September 14, 2014 at Cabo San Lucas on the southern tip of the Baja California peninsula as a Category 4 hurricane packing sustained wind speeds of 144 km/h. Tracking into the Gulf of California, the maximum wind speed fell to 113 km/h by the time the storm reached the town of Loreto located 375 km to the northeast later the same day. As it advanced from under a foot-print diameter of 600 km, the system's counter-clockwise rotation spun out storm bands with the strongest winds and wind-driven waves generated from its energetic right-front quadrant. Quite aside from damage to public and private property of concern to civil authorities, erosion due to coastal flooding and the direct impact of wave activity against natural shorelines is a separate issue of interest to physical geographers and marine geologists.

Outwash from uplands through flooded stream beds has the capacity not only to transport terrestrial sediments to the coast but also to reconfigure unconsolidated shore deposits such as beaches and estuary tidal bars. Moreover, rocky shorelines are subject to incremental erosion from repeated

storms and long-shore currents over time. A previous contribution from our team [2] focused on Holocene events during the last 10,000 years related to the physical erosion of rocky shores on Isla del Carmen, one of the larger fault-block islands in the gulf with 95% coverage by rocky shores. The laterally coherent coastal boulder bed (CBB) that resides 12-m above mean sea level on the east side of Isla del Carmen is distinct due its source from limestone strata vulnerable to storm waves on the outer lip of a marine terrace. Limestone accounts for only a small part of the rocky coast around that particular island, which is dominated by igneous rocks. Based on a coastal survey by Backus et al. (2009) using satellite imagery [3], igneous rocks are represented by granodiorite, andesite, basalt and other volcanic sediments to account for 34% of the shoreline in the western Gulf of California (including islands). By comparison, limestone amounts to only 7.5% of the whole.

An eye-witness account filmed during Hurricane Odile from a landmark home built into limestone cliffs north of Loreto at Ensenada Basilio recorded waves that crashed over coastal prominences at a height of 8 m above mean sea level [4]; see also Supplementary Materials. Horizontal rain reached the inner-most part of the residential compound set back from the cliff edge by some 45 m. At nearby Ensenada Almeja (Clam Bay), a north-oriented headland is formed by igneous rocks with a prominence falling from a high of 18 to 6 m above mean sea level at its distal tip. Theoretically, those cliffs are vulnerable to erosion from wave shock arriving from the east, during which winds from a tropical depression would cross from one side of the headland to the other. The object of this study is the asymmetrical boulder bed forming a semi-ring deposit exclusively on one side of the headland within Ensenada Almeja that partially restricts the bay's opening. This is the first analysis of its kind dealing with igneous rocks that form CBBs in the Gulf of California. Overall, a wide range of energy sources capable of rocky-shore erosion and CBB development include the daily tides, seasonal wind patterns that influence long-shore currents, episodic storms, and tsunamis. A secondary goal is to provide information on additional CBBs throughout the Gulf of California formed by igneous boulders. Common patterns in the physical geography of such features sugges<sup>t</sup> a novel approach forward in the study of CBBs within an active zone of subtropical storms impacting continental margins. Useful comparisons also are made with notable CBBs elsewhere in the world.
