Rio del Mar, CA Coastal Erosion Rate
Shoreline change 0.7 miles northwest of Rio del Mar, CA
Good news, and an honest one: USGS's data can't distinguish this stretch, 0.7 miles northwest of Rio del Mar, CA, from a flat trend. Whatever small movement it measured here is statistical noise, not a reliable direction, so none is claimed.
The grain of this number
USGS surveys the coast in transects spaced a few hundred feet apart; this page groups the nearest ones into a single ~3.5-mile reading for the stretch closest to Rio del Mar, CA, rather than showing one arbitrary line. Segment center: 36.96, -121.90. USGS's California assessment last surveyed this stretch through 1852-2016, computing the rate with its LRR method. Other US regions were surveyed in different years, sometimes decades apart, so this page states its own rather than implying one national vintage.
Where this fits nationally
This reading comes from 104 individual transects averaged together, 12% of which measured erosion rather than growth. The published margin on this reading runs ±0.51 ft/yr. The unadjusted figure here, 0.23 ft/yr, would place it 941 of 1211 if ranked directly - but an unreliable rank isn't a useful one, which is exactly why "no significant trend" is the headline instead. Source: USGS National Shoreline Change data release (ScienceBase, DOI 10.5066/P94J0K7Z), Kratzmann 2024 / Data Report 1187. Rank 1125 nationally for growth belongs to Coronado, CA, 401 miles from this stretch, measured at 1.22 ft/yr. Seacliff, CA, 1.8 miles off, is the adjacent measured stretch, itself no significant trend.
Not this whole stretch, just Rio del Mar itself: the Coastal Change Hazards Portal is USGS's own live version of this data.