*3.1. Data Collection*

Ensenada Almeja was visited on 28 and 29 April 2019, when the original data for this study were collected based on a sample of 100 boulders divided equally among four transects crossing the CBB. A Brunton compass and meter tape were used to lay out the transects, three of which conform to a N-S or E-W axis (Figure 2). The other transect was laid out parallel to the cliff line near the boundary fault. Various conventions exist for the differentiation of sedimentary clasts but the definition for a boulder followed in this exercise is that proposed by Wentworth (1922) for a clast equal to or greater than 256 mm in diameter [10]. No upper limit for this category is found in the geological literature, although Ruban et al. (2019) championed the term "megaclast" for boulders of extraordinary size [11]. That term is an appropriate descriptor for some of the boulders in the Almeja CBB.

The largest 25 boulders along each transect with centers spaced from 1 to 1.5 m apart were measured manually along three principle axes (long, intermediate and short). Triangular plots were employed to show variations in boulder shape, following the design of Sneed and Folk (1958) for river pebbles [12]. Data on the maximum and minimum lengths perpendicular to each other from individual boulders were fitted to bar graphs to show size variations from one transect to the next.

**Figure 2.** Northwest view across Ensenada Almeja coastal boulder bed (CBB) from an elevation of 16 m on the adjacent fault-bound headland formed by rhyolite bedrock (dog for scale on ridge).

A representative cobble of banded-rhyolite was collected from the Almeja CBB for laboratory treatment at Williams College, where it was weighed, and its volume determined as a function of equal displacement when submerged in a tank of water. Prior to immersion, the porous rhyolite sample was water-proofed by spraying it with Thompson's Water Seal TM (The Thompson's Co., Cleveland, OH, USA).

A DJI Phantom-2 drone TM (DJI, Nanshan District, Shenzhen, China) was flown over the Almeja headland and CBB to provide an overview of the study area and key reference points for construction of a detailed site map.
