The final cache coordinates are outside of the Mojave National Preserve. No physical containers have been placed in NPS land.
In order to find the coordinates for the final cache, you will need to visit 2 sites. The first is the summit of Clark Mountain. The second is a plane crash on the side of Clark Mountain.
FINAL LOCATION: N 35 30.AAA W 115 BC.DDD
Summit location (posted coordinates):
There is a 5 digit alpha-numeric code written on the inside of the ammo can at the summit. Add the number portion of that to 187 to get AAA. Example: If the code is GH194, then 194+187=381
Plane crash location (N35 31.536 W115 34.930):
When you get to the plane crash, on the fuselage, there is a 10 digit number in the format of XXX-XXXXX-XX (SEE SPOILER PIC). The 3rd & 4th digits are B&C. XXB-CXXXX-XX. To get DDD, subtract the last 3 digits from 462.
About the mountain (from SummitPost & Wikipedia):
Clark Mountain, at 7,933 feet, is the highest point in the Mojave National Preserve. This large and impressive mountain dominates the landscape near Mountain Pass for miles around. Although few people pay much attention to Clark Mountain itself, many are familiar with the long haul up Interstate 15 to Mountain Pass. The steep and sometimes treacherous grades of the highway as it crosses the mountain's southern flanks are usually enough to capture anyone's attention. Clark Mountain is located in the Mesquite Mountains BLM Wilderness Area. With a prominence of 4,254 feet, it stands out as the largest mountain around the area. Clark Mountain is also a world-class rock climbing area developed by Randy Leavitt in 1992. It has been described as containing the best limestone climbing in America, but we'll leave that for another day!
The higher elevations of the mountain are a striking sky island contrast to the lower elevations of the Mojave Desert vegetation. Creosote bush (Larrea tridentata), scrub and Joshua tree (Yucca brevifolia) forests grow on the foothills of the mountain while Single-leaf Pinyon Pine (Pinus monophylla), Utah juniper (Juniperus osteosperma), and White fir (Abies concolor) grow on the sky island at the highest elevations.
About the plane crash (from http://pacaeropress.websitetoolbox.com/post/Clark-Mountain-Navion-Site-Photos-2562351):
On March 2, 1951 Fred and Dorothy Elswit were killed when their rented Navion crashed in a snow storm on a flight from Las Vegas, Nevada to Santa Monica, California. The wreckage was discovered on March 3, 50 miles southwest of Las Vegas on snow covered Clark Mountain by Lt. Roscoe Anderson, a pilot from Fourth Air Force rescue squadron out of March AFB.