Pediocactus simpsonii Sevier Co. Ut.

Most seeds require oxygen to germinate, if buried too deep in their growing medium, or if the medium is too wet, the seeds may not get the oxygen they require.
Some seeds need to be in the light (surface sown) or in the dark (sown deep enough to receive little or no light) to germinate. A rule of thumb is to cover the seeds their own width deep in the growing medium, but some seeds prefer to be sown much deeper, and some fairly large seeds like to be surface sown (or higher).
Many seeds germinate best at certain temperatures, some will germinate at a comparatively wide range of temperatures, yet others need fluctuating temperatures.
Almost all seeds are waiting in a dormant state for some outside stimulus to break their dormancy, some just need sufficiently high ambiant humidity, others need scarification, vernalization or to be passed through the intestines of an animal.

Pediocactus simpsonii Sevier Co. Ut. seeds will usually germinate in 5-180 days, even under good conditions germination may be erratic.
Normally will only germinate with light so surface sow. Sow Pediocactus simpsonii Sevier Co. Ut. seeds on the surface of a Peaty seed sowing mix at about 25°C.

Sand, and loam, with some sphagnum moss or coir (coconut fiber/dust) make a good mix for germinating Pediocactus simpsonii Sevier Co. Ut. and similar seeds. The mix needs to be free-draining, and to be slightly water retentive. Surface sow the seeds and just cover with sand. Start germinating the seeds in shady (dark), humid conditions. As the seeds start to germinate, increase the light and decrease the humidity.

Cacti