Here is the full list of all 48 DiRT 4 achievements worth 1,000 gamerscore. It takes around 60-80 hours to unlock all of the achievements on Xbox One.
Completed all 12 Stages of a Monthly Event in Community Events
Finished in the Top Tier of a Delta Daily in Community Events
Finished a Stage in sunny conditions in Community Events
Completed back to back Weekly Community Events
Won the Triple Crown
Achieved 10 Gold medals in Joyride
Set a Gold medal time in a Time Attack challenge without hitting a penalty marker
Destroyed 100 blocks in 60 seconds in Joyride
Set a time in every challenge in a single Joyride Chapter
Won the Historic Legends Series
Earned the International Rally H-A licence
...it's gonna be a long week
Finished in the Second Tier or higher of a Daily in Community Events
Repaired your car on Stage and won the Stage
Completed an Event in Jam Session
Won the FIA World Rallycross Championship
Qualified in the top spot of a Rallycross Event in Career
Earned the International Off-Road C-1 licence
Earned the International Off-Road C-3 licence
Took two Joker Laps and won a Rallycross race
Completed a Stage or race with the Fearless Preset active
Won the Landrush World Series
Earned the National Stadium Pro-1 licence
Owned a vehicle equipped with all Grade A parts
Upgraded three Facilities to Grade A quality
Qualified for an A-Final in a Landrush Event in Career
Won the Global Rally Series
Hired a fourth Engineer onto your Team
Won a Stage in Headcam
Cleanly landed a jump longer than 65m
Completed all of the Advanced Driving Techniques at the DiRT Academy
Finished three sectors of a Stage with a flat tyre
Earned the International Rally R-1 licence
Earned the International Rally H-C licence
Won a Stage at night
Called in the Chief Engineer's recommendations during a Service Interval
Triumphed in the face of adversity
Earned the International Rally R-3 licence
Earned the National Stadium Pro-3 licence
Got an overall win in the lowest eligible Vehicle Class in a Rally Event in Career
Won your class in a multi-class Event in Career
Completed a clean Stage or race
Bought a vehicle from the Classifieds
Finished in first place in a Career Event
Earned the Fearless Bonus in a Stage or race
Completed the Welcome Event
Get promoted to a new Tier in Pro Tour
Complete 25 Events in Pro Tour