There’s an area in the cascade range (western US, specifically oregon) that is a giant field of knapped obsidian, that was used as a training ground for young knappers, as well as a trading ground to trade knapped obsidian that has been found all over the western US. Not just miles, but many many miles. I’ll see if I can go find a link.

A pretty typical 5th gear transmission ratio is somewhere in the 0.75:1 (engine rpm: transmission output shaft rpm) range, meaning the driveshaft would be rotating at somewhere around (definitely plus or minus) engine rpm. My subaru cruises at 50 at somewhere around the 2k rpm range, so the driveshaft would be spinning at a similar rpm. The diff pinion to ring gear ratio in the differential slows things down quite a bit so your wheels aren’t spinning at engine rpm anymore.