A threatened species

This lizard is threatened by development, agriculture, and other man-made intrusions into their small range. The majority of their remaining habitat in the US is administered by the Bureau of Land Management. The species (Phrynosoma mcallii) frequently coexists with sources of natural gas, oil, geothermal energy, and minerals which can found in its habitat.[6] In 1982, the US Fish and Wildlife Service declared P. mcallii as a Candidate 2 Category for the list of threatened and endangered species due to concerns over potential threats to their habitat which could further diminish the population. P. mcallii has also been given special status in both California and Arizona, which prevents their collection.[2]

Experiments have been conducted to investigate the "fluctuations in populations of flat-tailed horned lizards, Phrynosoma mcallii, in the Coachella Valley, California. This species has the smallest range of any horned lizard in the United States. In parts of its range, there are potentially conflicting activities, such as suburban development, agriculture, off-road recreation, and activities along the international border."[7]

Between 1978 and 1980 the Bureau of Land Management supported investigations of the status of P. mcallii in California. The purpose of this work was to determine the local distribution and relative abundance of P. mcallii, to correlate these parameters with various habitat attributes, and to gather information on the structure of the populations and mobility and food habits of individual lizards."[6]

The study also looked at the flat-tailed horned lizard's distribution and abundance throughout Arizona. The species was found to be restricted to an area of desert, 650–700 km2 in size, in the southwestern corner of the state. The species was most abundant in places with the Western whiptail (Cnemidophorus tigris), nests of the black harvester ant (Messor pergandei), galleta grass (Hilaria rigida) and sandy soils.[2]