Thornhill Drive Climb

We don't rate roads as safe or unsafe: crash counts can't say how risky a ride is, and roads people like to ride draw more riders, so they see more crashes. What the records show: no bike crashes were reported along the climb from 2021–2025.

How long and steep is the Thornhill Drive climb?

1.8 miles (2.9 km) at 6.6% on average, climbing 614 ft (187 m) from 568 ft to 1,181 ft. The steepest half kilometre averages 9.6%. That makes it a Category 3 climb.

Where does the climb start and finish?

It starts at 37.83333, -122.21392, where Thornhill Drive leaves Grisborne Avenue, and tops out at Snake Road at 37.8384, -122.20062.

Is Thornhill Drive paved?

Yes, by its OpenStreetMap tags.

How is the category worked out?

From the climb's shape only: length in metres × average grade (%) of 16,000 or more for Cat 3, 32,000 for Cat 2, 64,000 for Cat 1 and 80,000 for HC. It describes how hard the climb is, not traffic or crashes.

Where does this data come from?

The climb is found from OpenStreetMap roads and USGS 3DEP elevation (every climb, not a list of famous ones). Access is from OpenStreetMap tags; gates and closures change, so obey posted signs. Crash counts are police reports in the California Crash Reporting System (CCRS) on data.ca.gov, counted where their map location is within 100 ft of the climb. The forecast is from the National Weather Service.

• Colton BoulevardCat 3 · 1.3 mi at 8.7% · 614 ft · starts 0.3 mi away
• Snake RoadCat 3 · 1.9 mi at 6.7% · 659 ft · starts 0.7 mi away
• Shepherd Canyon RoadCat 3 · 1.8 mi at 6% · 577 ft · starts 0.7 mi away
• Ascot DriveCat 3 · 1.5 mi at 10.1% · 791 ft · starts 1.2 mi away
• Castle DriveCat 3 · 1.1 mi at 10.5% · 600 ft · starts 1.3 mi away
• Broadway TerraceCat 3 · 3.6 mi at 5.3% · 1,020 ft · starts 2.0 mi away
• Claremont AvenueCat 2 · 3.2 mi at 6.7% · 1,142 ft · starts 2.4 mi away
• Redwood Road from 35th AvenueCat 3 · 1.6 mi at 7.1% · 600 ft · starts 2.7 mi away