What could cause this...while driving on the interstate at 70 miles an hour I heard a noise like a cv shaft clunking then all 4 wheels locked up and iskidded for about 100 feet then they released but then had a loud clunking sound

Turn a tight right hand circle and listen for noise then turn a tight left hand circle and listen for noise. This checks the CV joints in the axles. Ujoints are cheap you might as well replace them while the shaft is off.

if it is front wheel drive that noise could be worn cv joints taking up the slack
if rear wheel drive it could be diff pinion to crown wheel clearance or side gear lash
take it to a drive line accredited service center that works on your make of vehicle and get a proper diagnosis and a quote
it could be a matter of idle rpms too high .

if the wheel alignment is faulty ( castor wobble ) at 70 mph there is no way that you can describe it as a vibration as it virtually rip the steering wheel out of your hands. If it is a torque converter problem then at around 3850-4025 rpm stationary there will be a vibration of the vehicle and engine The sort of vibration that you are experiencing at 70 mph will come from a drive line problem. If rear wheel drive then it could be faulty "U" joints, worn slip joint or failed rear engine mount
If front wheel drive it may be cv joints or bent drive shafts,wheel bearings or brake callipers not moving freely on the mounting bolts.

this might help:
Here is the Technical Service Bulletin that maybe of help, worth looking into but can't guarantee that it would fix your problem Steering - Steering Column Clunking When Turning TECHNICAL Bulletin No.: 01-02-32-001P Date: November 25, 2009 Subject: Clunk Felt/Noise Heard From Steering Column, Steering Gear and/or Front Of Vehicle During Turning Maneuver and/or Steering Wheel Rotation (Replace Intermediate Shaft As Directed) Models: 2001-2004 Buick Regal 2005-2008 Buick Allure (Canada Only), LaCrosse 2000-2008 Chevrolet Impala 2000-2007 Chevrolet Monte Carlo 1998-2002 Oldsmobile Intrigue 2004-2007 Pontiac Grand Prix Supercede: This bulletin is being revised to add the 2008 Buick LaCrosse/Allure. Please discard Corporate Bulletin Number 01-02-32-001O (Section 02 - Steering). Condition Some customers may comment on a clunk type noise coming from the front of the vehicle while driving during a turning maneuver.
1. Locate a large area (parking lot) where the vehicle can be turned in a tight circle. 2. Turn the steering wheel to the right and/or left all the way to the steering lock, then off the steering lock a 1/4 turn. 3. Drive the vehicle approximately 5 km/h (3 mph) in a circle, preferably over rough pavement or seams on the road surface. 4. Drive the vehicle straight ahead at idle speed while applying and releasing the brake pedal. Listen/feel the steering wheel for the clunk/noise condition. 5. If a clunk is felt in the steering wheel, the MOST likely cause is the I-shaft - not the steering gear. Continue with the correction. Correction DO THIS - Replace the intermediate shaft DON'T DO THIS - DO NOT lube the intermediate shaft Replace the existing intermediate shaft

this would be your cv axle the clunking is a sure sign ,its the same noise in all front wheel drive cars,if not fixed it can cause a number of other problems.this is your front drive axle.

You need to replace the CV shaft boots. They're cracked and leaking grease that keeps your wheel bearings and CV joints lubed. If you keep driving, extensive damage may occur creating more issues!

bad motor mounts will cause some issues, bad CV joints will also cause and issue. You will need to check for both. Being a 99 you will also want to check teh front differential for the proper fluid level, this is not the same as the transmission.

sounds like a broven cv shaft have you been hearing a clicking noise when turning this indicates a bad shaft or do you have bad motor mounts this can also cause cv failure

drive shaft constant velocity joint ,check rubber boot if ok then leave well alone because it will run for another 10,000 miles at least

Is it full time or part time 4 wheel drive? You should check the front driveshaft u-joints.