Probably the easiest way to get up Ysidrio peak.
Continue hiking on the dirt road, continue along the (dry) creek bed and pick up a dirt road heading east.
Keep west of the Thimble peak on the left (West) side of the drainage.
Eventually entering Anza-Borrego Desert State Park. (unsigned)
Ysidrio is right in front. Keep left in the drainage up to the corner of the Reservation. Keep out of the Reservation by heading East towards the peak.
Up to this point it's rather easy, now more rocks and scrubs. The scrubs are the obstacles toward the peak on this approach.
Closer to the peak a somewhat steep climb on granitic rock, than almost at the peak, sand and the hike is real easy again.
The peak itself isn't that obvious, probably slightly higher than the other boulders.
Finding the marker on top of the peak boulder is the ultimate proof, this is the right place.
Going back on a more easterly route towards a saddle. This lacks all the obstacles, but is slightly steeper, but it's mostly sand with some rocks.
Once close to the saddle find a route avoiding the scrubs and head South/West.
There is a small bump in the elevation plot, in actuality the climb is rather gradually at that point.
Warning:
The first part is BLM so shooting is allowed.