BETA — measurements and names under active refinement. Seen a sign, a gate, or a better name? Submit an update no account needed · photos welcome via GitHub

Upper Grassy Hill Road

5468.9 m · net rise 190.8 m · total ascent 219.3 m · overall 3.5% · confidence: high · Southbury · Connecticut · share

Shape: stepped — 58% of the climbing sits in a quarter of the distance; longest continuous stretch at 10%+ is 206 m.

Found purely from mapping and LiDAR data, and not yet matched against books, race records or lists — it may be well known to locals under a name we've never heard. It was cross-checked against the OS road network, surface models and map tags, but a discovery can still be an artifact of the terrain model or the map. Treat it as a well-evidenced hypothesis until someone has ridden it. If you know this road, tell us what you found — photographs, corrections and local knowledge all welcome; the map links below let you scout it first.

Gradient ladder what do windows mean?

Window	Maximum	Located at
2 m (diagnostic)	21%	158–160 m
3 m (diagnostic)	21%	157–160 m
5 m	20%	154–159 m
10 m	20%	153–163 m
20 m	20.1%	145–165 m
25 m	19.8%	145–170 m
50 m	19.3%	116–166 m
100 m	18.8%	70–170 m

may_start_earlier Extent detection suggests reviewing where this climb starts/ends.

Map

Check this route yourself: Google Maps route via their router · Street View at the base where coverage exists · geojson.io our exact measured line · OpenTopoMap

This climb's data: OCL JSON — the full gradient ladder, quality flags and provenance in the OpenClimb Ladder format.

Measured, not vetted. This page records what the laser record shows about the road's shape — nothing more. Nobody has necessarily ridden or inspected this road for the survey, and a page here is not a recommendation and no guarantee that the road is open, surfaced, rideable or safe. Gates, private sections, missing rights of way and hazards do not show up in elevation data. Check access and conditions on the ground and make your own judgment.

Ridden it, or know better? Submit data for this climb no account needed · Share this climb

Upper Grassy Hill Road LiDAR hillshade map with contours

Profile

Provenance

{
  "analysis_version": "0.1.0",
  "sample_interval_m": 1.0,
  "interpolation": "bilinear",
  "smoothing": "none",
  "gradient_windows_m": [
    5.0,
    10.0,
    20.0,
    25.0,
    50.0,
    100.0
  ],
  "diagnostic_windows_m": [
    2.0,
    3.0
  ],
  "elevation_crs": "EPSG:26918",
  "elevation_resolution_m": 1.0,
  "elevation_tiles": [
    "data/cache/usa/ct/USGS_1M_18_x64y460_CT_Statewide_C16.tif",
    "data/cache/usa/ct/USGS_1M_18_x64y461_CT_Statewide_C16.tif"
  ],
  "calculated_at": "2026-08-24T21:37:27+00:00",
  "road_source": "OpenStreetMap (local PBF extract)",
  "road_attribution": "\u00a9 OpenStreetMap contributors, ODbL",
  "osm_pbf_path": "data/cache/pbf/connecticut-2026-08-23.osm.pbf",
  "osm_snapshot": "2026-08-22T20:21:28Z",
  "run_id": "redo-ct-1-260824",
  "elevation_provider": "USGS 3DEP (The National Map)",
  "elevation_licence": "Public domain \u2014 USGS 3DEP 1 m DEM, courtesy of the U.S. Geological Survey",
  "elevation_dataset": "USGS 3DEP 1 m DEM, CT_Statewide_C16 (collected 2016)",
  "elevation_tile_ids": [
    "x64y460",
    "x64y461"
  ],
  "climb_origin": "discovered",
  "notes": "Coarse pass: max 15.8% over 200 m (Terrain 50), gain 191.0 m over 5469 m way. KEPT at seed extent: no ascending continuation (min_avg=2.0%). ADOPTED (NE wave 1, 2026-08-25): big-gain. Wales dials per PRODUCTION 'US ADOPTION DIALS'.",
  "canopy_check": "unavailable \u2014 no surface model (DSM or point cloud) registered for this coverage",
  "license": "ODbL-1.0",
  "license_url": "https://howsteep.org/licensing.html"
}