According to https://snowbrains.com/8736-ebbetts-...or-the-summer/

Some research found https://www.uniondemocrat.com/news/a...bcf7cf98e.html (from 2020 - note they only let you see 5 articles for free) that includes:

"Opening dates for Sonora Pass over the past five years were May 30 in 2019, May 3 in 2018, June 13 in 2017, May 18 in 2016, and April 17 in 2015, which was also the earliest opening in the past 10 years and the height of the historic drought from 2011 to 2017.

The opening dates for Ebbetts Pass over the past five years were May 30 in 2019, May 4 in 2018, June 30 in 2017, May 13 in 2016, and April 17 in 2015."

Note that 2017 and 2019 where both Springs with deep snowpacks and late opening of Sierra passes. Also while top of Ebbetts is nearly 1,000' lower than Sonora that due to steepness Sonora does not have many miles above 7,500'. Ebbetts is narrow and climbs to 8,050', then drops to Pacific Valley at 7,600' before climbing again to pass at over 8,730'.