The Pyrenees. The Alps. The Jura Mountains?? Wikipedia notes:
“The Jura Mountains . . . French: Massif du Jura, (German: Juragebirge, Italian: Massiccio del Giura) are a sub-alpine mountain range located north of the Western Alps, mainly following the course of the France–Switzerland border. The Jura separates the Rhine and Rhône basins, forming part of the watershed of each.
The name "Jura" is derived from juria, a Latinized form of a Celtic stem jor- "forest". The mountain range gives its name to the French department of Jura, the Swiss Canton of Jura, the Jurassic period of the geologic timescale, and the Montes Jura of the Moon.” Wikipedia
The Jura mountain range runs in an arc along the eastern edge of central France and the western edge of Switzerland. To orient ourselves very generally, using Lake Geneva as a reference point, the mountain range starts in France to the southwest of Lake Geneva and arcs above Lake Geneva, ending to the northeast of it. Here is a crude PJAMMCycling effort at marking the mountain range:
This mountain range is home to some of the most difficult bike climbs in Europe outside of the Pyrenees and Alps. Little known in the U.S., this mountain range is poised to burst onto the climbing scene, if it has not already done so. Col du Grand Colombier initially became well known to cyclists via the Tour de l'Ain (late season professional cycling race held generally in eastern France). From what we can tell from our research, Col du Colombiere has been included in the Tour de France first in 2012 (stage 10) and again 2016 (stage 15).
PJAMM rode the 4 routes to Col du Grand Colombier on May 29 and May 30, 2018:
From Culoz (south; pop. 3,029, 2014 ): This seems to be the most popular side (per our review of Strava ascents from all 4 sides) and by our observation, the most scenic. We have exceptional views of the valley and Le Rhône River (one of the major rivers of Europe).
The roadway from Culoz to the Col is excellent and markers are placed ever kilometer from the bottom of the climb to the top.
From Artemare (west; pop. 1,210, 2015): Subjectively we felt this was the hardest of the 4 climbs. Our hunch was verified by reference to the Fiets index which had Artemare ranked above the other 3 routes to the Col. The average grade for a 4 kilometer stretch just past the midpoint of the climb is 12% and hits 19% at one spot between 10 and 11 kilometers.
We are surrounded by forest from 7.5 to 13.6 kilometers before the surrounding open (in late may anyway) to fields of wildflowers.
From Anglefort (northeast; pop. 1,133, 2015): We are surrounded by trees much of this climb. The Anglefort route intersects the rouet from Culoz at kilometer 6.2 and thereafter the 2 routes share the last 8.8 km, 610 m ascent at 8% average grade.
Intersection of Anglefort and Culoz routes
From Lochieu (northwest; pop. 93, 2015): This route intersects Artemere at km 7 (Point de vue du Colombier). As with the other routes to the Col, we are surrounded by trees much of this climb.